johnsmachines

machines which I have made, am making, or intend to make, and some other stuff. If you find this site interesting, please leave a comment.

Category: CNC lathe

Boxford TCL125 CNC Lathe, 3rd AXIS.

Below is a video which was recorded by my machining mentor friend, Stuart Tankard.  Stuart made a milling attachment for his Boxford CNC lathe, and he demonstrates it in the following video by making some lovely small valve control handles.

I followed in Stuart’s footsteps by making a similar attachment for my identical Boxford 125 CNC lathe, but I have not yet video’d it in action.  Not much point when Stuart’s video is so good.  I really like the absence of irrelevant, irritating music.  Just machining sounds.   Enjoy.   (if you want to see it full screen, copy the YouTube address from the settings icon).

Model Cannon Barrel. (T)rifling Thoughts.

My aim (as it were) in making this model cannon is to have a high visual quality exhibition piece.

It is a 1:10 scale model, 1866 Armstrong 80lb, rifled muzzle loader, blackpowder cannon.

One question which always arises is whether it will be actually fired.  My answer is that if it could be fired legally, it would be nice so I could make a video.  However, Australia has very strict gun control laws, (with which I totally agree), and I do not intend to flout those laws.  So this gun will not be capable of being fired.  It will have no touch hole.

To satisfy the visual appearance of a touch hole there will be a laser printed dot at the location.  Along with laser engraved Queen Victoria insignia, sight lines, etc.

But, it IS a rifled cannon, so I do intend to rifle the barrel.  And that needs to accomplished before the trunnions are fitted, and after the cascabel is fitted, so the orientation of the rifling is as per the original.

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The original rifling.  The 3 grooves are each 30mm wide, (clockwise or anticlockwise, not sure) and extend up to the edge of the powder chamber.  They are about 2 mm deep.  The powder chamber is slightly wider than the barrel bore, being continuous with the depth of the rifling grooves.  It is academic, because it will not be visible, but I will make it (the powder chamber, and the whole model) as accurately as I can, for my own satisfaction.  Fortunately the powder chamber is accessible to machining from the breech end, because the cascabel is screwed into position, and is removable.

Yesterday I started making the cascabel.  It was difficult.  The steel thread is lathe cut first, then the shape is lathe CNC’d.  Then there is milling the insides, and making a removable pinned rope retainer.  The third attempt was the most successful, but I am still not satisfied, and so there will be another one made today.   This is what I have so far…

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The turned barrel, threaded to accept the cascabel.  More work is required on the cascabel.

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The cascabel is mounted in an ER40 chuck.  It has been drilled and milled, and a removable insert is temporarily glued into place pending more machining.

 

Rifling.  Searching YouTube reveals multiple tools and setups from US sites.  Here are a few screen shots to show you some varieties.

From the sublime ….

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to the other extreme…

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No.  I will not be using a PVC pipe lash up.

The amateur designed and built machines are interesting….

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Sine bar on the right.

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Then there is the method of pressing a button cutter through the bore.  My bore is an odd size, so if I used this method I would need to make my own cutter.

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This one is a computer animation of a 19th century rifling machine, now a museum exhibit.   Can you see the barrel?   Armstrong probably used a much larger version of this type to rifle his cannons.

 

But I think that I will use none of these methods.  I have a CNC mill and a CNC rotary table.  Mach3 can control both of these machines simultaneously.   If I mount the cutter assembly in the rotary table, and the cannon barrel to the mill quill, I should be able to cut the rifling grooves.  Still working on this one.

Armstrong RML barrel

After 3D printing a plastic 1:10 barrel I decided to have a go at turning one in steel.  I had a length of steel 70mm diameter and 290mm long, which was just too short to turn the entire barrel, so I decided to make one of the breech reduction rings separately, when I make the cascabel.

I did not know what the steel grade was, but it was off a machine so I thought that there would be a good chance that it would be reasonable quality.

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The length of rod next to the printed barrel.

The turning was initially fairly routine.

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and I was really pleased with the finish which was appearing.

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Mountains of hot swarf.

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The roughed out barrel.  I used the 16mm drill bit to drill the bore from both ends, but there was still 50mm or so beyond the reach of the bit.  So I silver soldered the drill bit into a length of silver steel (drill rod).

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And quickly completed the drilled hole. 

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Then transferred the piece to the CNC lathe, and shaped the barrel exterior.

I experienced 2 problems with the CNC turning.  The tapered chase of the barrel, and the rounded fillets came out really well, but the straight sections of the breech developed chatter marks.  I was preparing to take a skim to remove the chatter marks when I bumped the manual CNC control, the cutter dug in, and I got a deep score in the breech.  And broke the carbide cutter.  I turned away the dig in, but it left the breech diameter 3.5mm undersize.

I have no more steel of that size, and it will be quite a while before I get an opportunity to buy some.  So I persisted with the slightly undersized barrel.  It will be 62mm diameter rather than the intended 65.5mm.   I still have not decided whether to scrap it and start again.  But if I can get some more suitable steel I will remake it.  I might even use the undersized barrel to make a 64lb Armstrong RML, which had a smaller diameter breech than the 80lb RML which I am making.

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I showed it to SWMBO.  “That is beautiful” she said, somewhat to my surprise, and being surprised by its 3.5kg weight. 

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Ah…  if only…

Lathe Toolpost Milling attachment (CNC)

 

Although my recent posts indicate that I have spent  a fair amount of time recently on Google Earth Pro, I have also been busy in the workshop.  Mainly finishing the toolpost milling attachment for the Boxford CNC lathe, but also fiddling with the laser attachment for the CNC mill.  Neither of those projects is completely finished, but I thought that you might be interested in some progress photos.

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This is what the Boxford TCL125 CNC lathe now looks like from the front.  It is substantially modified from the original which I purchased 5 years ago.  To mention a few changes…..

the axis stepper motors are bigger and more powerful than the originals

the ball screws are now 10mm diameter, compared with the original 8mm

there are some adjustable axis limit switches

the 3 jaw chuck is replaced by an ER32 collet chuck

there is a removable toolpost milling attachment with ER 16 Collet chuck, with a speed controller, cables, and panic switch.

there is a removable safety screen (not seen in the photo)

And hidden in the electronics compartment….

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There is a 750 watt AC Servo spindle motor and controller (RHS, under the coiled cable)

The electronics have been replaced with a Mach3 compatible breakout board and associated peripherals.  Anyone with an original 1985 machine will hardly recognise these components.

And the software is now Mach3, running off an old Windows XP computer.  And using “Ezilathe” for most of the G coding, especially threading, and interpreting shapes which have been drawn as CAD dxf’s.

The new toolpost spindle works, but the software  needs a bit more fiddling to tie it into the CNC controls of the lathe.

The Boxford has provided an excellent base on which to make these changes, and I look forward to producing some videos soon of the renewed machine in action.

 

CNC Lathe Toolpost Mill

Just a quickie to show you a progress photo of my current project.

It is a very small milling motor with a small ER collet, mounted onto the toolpost of my Boxford CNC lathe, which will convert the lathe from 2 to 3 axes.

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At this early stage the toolpost holder and cylindrical motor have been mounted to the water jet cut bracket on the right side.  Pulleys and drive belt yet to be fitted and I will trim the shaft at the left hand end of the motor.  Then the motor wires are connected to a speed and direction and on-off controller.

The usefulness of this tool is apparent in the following video of a completed unit in use.  The main spindle motor of the lathe is now a 750w AC servo motor, which can be controlled from Mach 3, to go to programmed positions and hold the position while a milling procedure takes place.  Of course the milling procedure will be with small cutters or drills, perhaps up to 3-4mm diameter.

The idea, plans, and some of the parts are courtesy of Stuart Tankard, my very clever friend, whose completed machine is the subject of the following video.

Stuart’s video is republished here with permission.  The original, with comments, is visible on YouTube.  If you have technical questions about the setup, I suggest that you contact Stuart via his YouTube post.

Another axis for the Boxford 125TCL

Watch the video of Stuart Tankard making tiny valve handles on his CNC lathe.  Changing the old Boxford spindle motor to a new generation servo motor allows him to use Mach3 to control the spindle to turn very slowly and to a set number of degrees, producing the very attractive handle cut-outs and rim dimples.  i.e. he has added the functionality of an indexing head to his CNC lathe.

It required adding a small milling head and motor to the toolpost.

I can see one of these on my Boxford 125TCL in the near future.

New Spindle Motor for the Boxford 125TCL CNC lathe.

Reader Ben asked about the spindle motor replacement on the Boxford.   This is a small CNC lathe, and was often used for teaching in secondary schools in Australia.  Mine was made in 1985, and I replaced the electronics a few years back because they were obsolete and not functioning.  The mechanicals of the lathe were beautifully made and in excellent condition.  I did replace the ball screws, but in retrospect, that was probably unnecessary.   I also installed new and bigger axis stepper motors.

I was still getting some unreliable results, despite the the upgrades, and wondered whether the spindle motor was lacking power.  I was taking lighter cuts to try and cope but clearly a new spindle motor was required.

The space that the motor occupies is fairly tight, and initial searches for a suitable replacement were fruitless.  The new  ClearPath motors looked promising, but enquiries to the manufacturer indicated that the required power and rpm’s were not available.  Then my expert friend (or should that be “friend who is an expert”?), spotted the Ebay ad below, and bought and succesfully installed the servo motor in his 125TCL, so I did likewise.  I am afraid that the electronic aspects remain a mystery to me, so I cannot help with those.  It is a 0.75kW motor, substantially more powerful than the original, but very compact.

 

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Do an Ebay search on the code on the controller.  I paid $AUD339 but it is now plus postage and GST, so close to $AUD400

 

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The new spindle motor and servo controller

 

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A new motor pulley was required.  There is still a high and low belt ratio available, but with the extra power and torque I never use the low ratio.  RPM range is 300-3200.

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This has been a very successful modification.

Many thanks to Stuart Tankard for his generosity in time, expertise and advice in getting it going.

 

 

 

 

More Wierd Stuff

Since my “Strange Lights over Geelong” experience I have been looking at all sorts of weird posts on YouTube.  UFO’s, crop circles, megalith structures, evidence of buildings on the moon and on Mars.  There is a mountain of information out there, and while a lot of it is lies and rubbish, some is harder to dismiss.   It is not inconceiveable that Governments have information which they are witholding from the general populace, about aliens, UFO’s, ancient civilisations and so on.  Indeed, there are YouTube interviews with ex astronauts about UFO’s on the moon, and ex government ministers and officials about UFO’s and aliens, and Rothwell.  It may well be that the current increased talkativeness is due to a recognition by governments that they can no longer keep a lid on the previously secret information, so they are gradually allowing people to talk.

One line of posts which I have followed is evidence that something is going on in Antarctica.

And one source of information is Google Earth.  One post related to a strange set of giant “steps”.  I checked on the post information by checking the coordinates in Google Earth.

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Look at the middle of the photo.  That series of “steps” does look unusual.  You can check on this yourself by entering the coordinates on the photo into Google Earth.   The “staircase is about 2.5km long, with each step about 250 meters.

Anyway, to continue with my story, as I was zooming out from this point, I noticed a bright shape about 138km towards the south.

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The object which caught my eye was the white rectangle above the word “Coast”.  This section of Antarctica is directly south of Western Australia.  The rectangle is about 380 km from the coast.

And this is what shows up on Google Earth as I zoomed in.

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The image is from 1999.  The black rectangle is 21 x 7km…  Quite a size!   I am unsure what the bright white is.  Possibly sunlight reflecting off a shiny surface.  Or a rough attempt at concealing the rectangular area?    This is at latitude 70.2 S, longitude  87.2 E.

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Also, there is a faint streak from the rectangle heading about 100km to the east.  It is also 7km wide.     The staircase area is also visible to the north.

So that is it.  I can find no reference to this structure, but if anyone knows anything about it, please enlighten me.   If you have any interest in this weird stuff, you might the posts on YouTube by SecureTeam10 worth watching.

I am heading back into the workshop tomorrow.  Installing a steam powered boiler water injector on the Fowler traction engine, and bit by bit, finishing the triple expansion engine.

I have installed the new AC Servo motor to replace the spindle motor on the Boxford 125TCL CNC lathe, my expert friend Stuart Tankard has wired it up and reconfigured Mach3.  I am delighted to report that it has vastly improved the CNC lathe.  Will post some pics in a day or two.

A New Spindle Motor for Boxford 125TCL CNC lathe.

The spindle motor on my 33 year old Boxford CNC lathe has struggled to machine steel, although it copes with brass OK.  My expert friend has recently upgraded his machine (identical to mine) with a new spindle motor, and I will do likewise.

The new motor is a 750 watt Servo, bought on Ebay from China.

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It is more powerful than the original DC motor, small enough to fit the limited space in the 125TCL, and my friend reports that it is performing very well indeed.

Some modifications to the mounting system and drive pulleys and electronic controls will be required.

For reader Tom, who is upgrading a 125TCL as a school project, I include the following photo.

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On-off switch of the 125TCL.

Boxford 125TCL CNC Upgrade

This small CNC lathe was converted from the original c1985 electronics, to components which are compatible with a PC running Windows XP and Mach3.

Reader Paul M asked about circuit diagrams.  I must confess that I do not have such.  Indeed, I would not understand them.  The electronic connections were made by my expert friend Stuart T.   I believe that Stuart intends to write up the conversion for one of the Australian magazines, and possibly this post might give him a gentle shove~.

In passing, I should give Stuart a thumbs up for his excellent CNC lathe program, which is far superior, in my opinion, than Mach3 for running the CNC lathe.  It is called Ezilathe and is available as a free download.

Anyway Paul, here are the promised photographs of the electronic components of the Boxford, after the conversion.  You should be able to work out many of the connections by zooming in.

 

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The Boxford 125TCL sitting on a bought trolley which could have been made to measure.  The PC is on the bottom shelf, the extra toolholders and tools in the drawers, the wireless MPG on the front, and upgraded stepper motors in black.

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The rear view to show the extra power outlets to supply the screen and PC.  I still operate this lathe in a spare bedroom of my house.  Very handy if I have a sleepless night.  It is so quiet that it does not disturb SWMBO.

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The view with the back open.  The only components from the original setup are the spindle motor, the main switch, and the Gemini controller (RHS with orange cover).

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Power outlets, main switch and power supply.

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Transformer.  Can’t remember what the Fotek is for.

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Gemini with cover removed.

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C11 R9 Breakout board, the optical indexer (top), and Gecko stepper drivers (LHS), parallel cable from the PC,  all mounted on an aluminium plate.

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Spindle motor, original.  But now considering upgrading to a more powerful motor.

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new cable junction box for the stepper cables.

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New cooling fan, top LHS

So, I hope that these shots are some use.  If you do not recognise the components, I suggest that you follow my example and bribe an expert friend to do the connections.

Making Hubcaps

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I made 5 of these

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The 50mm diameter aluminium blank had a 12mm bolt inserted into a blind threaded hole.  The bolt was held in the lathe chuck.

The 2 short videos which follow show 1. the final rough cut 2. the finish cut.

The shape was drawn as a DXF file using CAD, the G code was generated using Ezilathe, and the lathe was controlled with Mach3.

 

 

Total CNC turning time was 16 minutes per hubcap, plus cutting the groove for the O-ring, then a quick polish with a cleaning pad.

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Another little job for my CNC lathe.

A fellow club member asked me to turn some hub caps for his car restoration.  And the shape was a bit unusual.

This is the first effort at complying with his request.

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It is aluminium, and will be held in position with an O-ring in the groove.

If I had put a knife edge on it he could have justified new car number plates…..

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Metalworking for a cabinet maker

Our model engineering club has been locked out of our club rooms because MOULD has been detected in the building.   Apparently a lengthy process to reduce the mould to acceptable levels.  (note to self…. make sure that the inspectors never set foot in our house).

So our meetings have been held in various locations, including a sports centre and a basketball building.   I feel quite virtuous when I enter these buildings, but for some reason I do not feel any fitter when I exit.

A recent day meeting was held at my farm workshop.  Not my farm anymore, just the buildings.

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Not that one….   the other one.

And one of our more senior members requested a display of CNC machining, from design to product.

So, I drew up a finial which was required to complete a bookcase which I had built 30 years ago.  Then imported the DXF drawing file into “Ezilathe”.

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Showing Stuart Tankard, the author of Ezilathe, scrutinizing my drawing ….  and offering excellent suggestions for improvement using Ezilathe.

Then used Ezilathe to generate the G codes…..

Then to the CNC lathe…..

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CNC turning the finial in 51mm brass rod.  1600rpm, 100mm/min.  Controlled by Mach 3 Turn.  I removed the tailstock shortly after this photo was taken, to permit completion of the ball.

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Some GSMEE members watching the CNC turning.  I spent 3 days clearing up the workshop so the 16 members could fit in.   Amazing how much space was revealed in the workshop.   This is the Taiwanese lathe which I converted to CNC.  See old posts for details of the conversion.

I watched anxiously as the part was gradually revealed.  Admittedly, I had had a test run in wood to check the parameters, but this was the first run in metal.

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The finial.  The bar stock was parted later.

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Bookcase finally finished, after 30 years.

If you are interested in CNC lathe work, you should take a look at “Ezilathe”.  It is superb.

If you are on Facebook, (of course you are if you are reading this), you might like to take a look at the GSMEE Facebook site.

 

NEW SPINDLE MOTOR for CNC LATHE?

Now that I have replaced the stepper motors in the Boxford CNC lathe, (see “New steppers for an old CNC lathe”)  I am considering whether I might replace the spindle motor for the same reason…  that it has become less powerful due to the age of its permanent magnets.   Sometimes I am aware that it struggles to keep up the revs while cutting.

Watch the YouTube video about the next generation servo motors.  They use modern rare earth magnets.  They are powerful, compact and precise.  And not cheap.  Stuart T, who has the same Boxford CNC lathe as me, has suggested that these Clearpath motors would be suitable replacements for the ageing Boxford spindle motors .

 

 

 

The Robert the Bruce approach to turning problems.

Robert the Bruce was watching a spider making a web in the cave they were sharing, so the story goes.  The spider tried 6 times to make a difficult connection, and on the 7th attempt, it succeeded.  Robert, who had tried many times to become king of the Scots, was inspired to try yet again, and he did indeed become King Robert 1 of Scotland, eventually.

I thought of Robert more than once recently, when I was making an ER40 collet chuck for my CNC lathe.  The particular  collet chuck involved making a 2.25″ x 8tpi internal thread, a 50mm x 1.5mm external thread, and cutting an 8 degree internal taper.   Not too complicated you say.  I agree, but for the chuck to be useful, each step had to be extremely accurate.

I made 4 successive collet chucks until one was adequately accurate.

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CHUCK 1, 2 and 3

Chuck 1 actually went very well.   Nice tight spindle thread, taper good, and external thread just right.  But the chuck did not quite seat firmly.  Could it be that the spindle thread (the internal one) was not quite long enough?   So I cut a deep distal groove.    Wound out the carriage.   Oh shit!   Forgot to clear the spindle thread.   Totally destroyed it.   The chuck actually fitted the spindle quite nicely, but with only 10% of the thread remaining, it was useless.

Chuck 2 was made in 2 pieces, on suggestion from Stuart T.  The idea being that if there was any inaccuracy in the lateral runout, the piece with the taper could be adjusted.  OK.   Sounded sensible.  Again all went well, but the spindle thread was not correct.  For some reason the thread cutter seemed to make a new path about half way through making the thread.   So the spindle thread was thinned  excessively.   But still tight.   So I made the tapered half, and joined it all together.  Fitted it to the lathe and measured the runout and taper.  All good.  Less than 0.01mm runout and perfectly parallel to 100mm from the chuck face.   But.   The next day I removed the chuck, replaced it, and did the runout measurements again.  I did not need a gauge.  I could see the wobble.  Chucked the chuck  into the rubbish bin.  That thinnned out spindle thread was hopeless.   But what caused the problem?  The thread was CNC cut, and it should have been perfect.

So chuck 3.   One piece again.    All seemed to go well, but again the big spindle thread was wrong.    Again there seemed to be 2 thread paths.

Then the penny dropped.   The spider made the web connection.   Robert got the throne and John saw the light.

The tool post had moved slightly during the threading!  It had twisted a little, as a result of the T piece in the carriage slipping.  F**K    F**K  F**K!!!

I replaced the T piece grub screws with more solid cap screws, and really tightened them.  Then made another chuck.    I must point out that each chuck was about 6-8 hours of machining, normally a very pleasant time.  But by this time, I felt like that  bloody spider in the cave.

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ER40 Chuck Number 4.

One advantage of making 4 chucks is that each one was made faster, and with more confidence.   This one was made in about 5-6 hours, including painting with selenium oxide to give it a black appearance.

It has a runout at the chuck face of 0 – 0.01mm (which might have been due to inaccuracy in the rod which was being measured), and a taper of 0.02mm at 50mm from the chuck face.  It feels nice and tight when being screwed on.   OK,  Success.   Eventually.

Next job, the throne of Scotland.

But obviously that slipping top slide on the CNC lathe has to follow chucks 1,2 and 3 into the rubbish bin.   It will be replaced by a fixed, immoveable tool post.

New Steppers for an old CNC Lathe

My Boxford TCL125 CNC lathe was missing steps in the cross slide, with resulting inaccurate work.  Obvious causes, like cutters not sharp, or gibs too tight were excluded.  Changes in the stepper motor settings maybe helped a bit, but not enough.

Stuart T suggested replacing the stepper motor, since the machine is a 1985 model, and the steppers look original, and therefore the 32 year old stepper permanent magnets are probably not as strong as they were originally.

We had changed the electronic controls in the lathe 3 or 4 years ago, so it would work with a Windows PC, and Mach3.  Mostly I use “Easylathe” for generating the G codes.

Stuart had a spare stepper motor in his junk box, and it was the correct size (Nema 23), but more powerful than original.  So I swapped it, and missing steps disappeared.  Hooray!  A minor problem was that Stuart’s stepper had shafts at both ends, and I was not comfortable about cutting off the unwanted shaft end, and I had decided to change the Z axis stepper also , so I ordered some new stepper motors.

A carton of 3 motors arrived a few days after placing the order.  They are made in China, and are nicely finished.  Each new motor had 4 wires, whereas the originals had 8 wires each, but reference to the wiring diagrams quickly determined the connections.  Total cost for the 3 motors was $AUD90, including postage, and now I have a spare.

A big advantage of the NEMA mounting system is that the motor mounting dimensions are fixed, so swapping motors is simple.  More powerful stepper motors are longer, but the dimensions are all available online, and can be checked before ordering.

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The black and silver new stepper motors fitted to the Boxford TCL125.  One cover waiting to be reinstalled.

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The old steppers on the right.   

A simple CNC turning test worked well, so I am hopeful that this problem is fixed.

 

Model Ottoman Bombard – Painting

I would have preferred that the title of this blog was “Finishing the Ottoman Bombard”, but I am still waiting for the vectors of the barrel mouth decorations and Arabic (?) writing, and the touch hole.

But I have at least painted the bombard, and the pictures follow.  You will notice that I have not attempted to reproduce the bronze or copper colours of the orginal in Fort Nelson.  Partly because I doubted my ability to make painting such variegated patterns realistic, and partly because the cannon would not have looked like that in its heyday of 1464.  It would probably have been either black, like most SBML cannons (smooth bore muzzle loading), or possibly gaudy golds and reds and blues like other medieval items.  So I painted it black.  I like it.  If I get evidence that it should be more colourful I can change it later.

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First coat – Primer.  Hmmm… interesting colour.

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Next coat – matt black brushed on, to fill the hairline wood cracks.  Incidentally, the (dirty) parquetry floor is also made from the red gum house stumps from which the cannon is made.

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final two coats –  matt black, from a spray can. 

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So there it is, finished except for the barrel mouth engraving, and the touch hole.  Now what to do with it…   SWMBO says it might be useful as an umbrella stand.

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The breech.  25mm diameter explosion chamber.  1:10 scale

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The barrel, 63mm bore.

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Assembled.  The model is 520mm long.

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It does need some decoration

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Modelling a Turkish Bombard -4 Decoration

The decoration around the barrel is formed by a repeating pattern, which when milled, very cleverly forms 2 identical patterns.  One is excavated and one is the original barrel surface.  You will see what I mean if you look at the pictures in the earlier blog, and the video below.

It took me an evening of experimenting on the computer to work out the system and draw it.

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Then I measured the diameters of the 2 gun components, calculated the circumference, (OK it is not rocket science.   3.142 times diameter), then working out the number of identical shapes which would fit around the 2 different diameters, at the same size and spacing.   Amazingly, it took 18 shapes to fit almost exactly around the barrel, and 16 of identical size almost exactly around the breech.  the angular spacing was 20 degrees and 22.5 degrees.

Then the shape was imported into V-Carve Pro, and G codes were generated.

My CNC mill does not have a 4th axis, so I used a dividing head to move the workpiece at the precise angles.  See the setup in the video.  That meant that the pattern was engraved into 16 and 18 flat surfaces, rather than a continuous cylinder as on the original.

It worked very well.  There were minor compromises due to the shapes being milled with a fine end mill but when you look at the pics I hope that you will agree that it is effective.

I calculated that the milling had to be at a maximum depth of 2mm in order to cope with the curvature, but if I do it again,  I would reduce the depth by 25%.

The first part of the video is a shot of CNC drilling.  Then the CNC routing of the repeating patterns.  Each angular setting of the pattern took 4 minutes to complete.  136 minutes altogether.  In reality, it took a whole day, most of which was spent doing the setups.

 

 

Bombard Model-3 turning the barrel

Another session or two, and this project is complete.

Now how do I make a cannon ball 62-63 mm diameter?  In wood will be ok?  Does not have to be granite.  I could make a mould and cast it in aluminium or lead, but stone would be authentic…..   thinking.

ps.  Re cannon balls.  I will cast them, in cement!   Now, how to make a mould.

Bombard Model -2. Big Thread

The breech and the barrel are joined with a very large thread.  On my 1:10 scale model it is 60mm diameter, and has a pitch of 6 mm.  These dimensions are measured off Internet photos of the original bombard, so they might not be faithfully accurate to the original bombard.  If anyone has accurate plans of the bombard I would be very interested to hear from them.

I experimented with various spindle speeds, feed rates, depth of cut, and finally decided that red gum wood is not the ideal material to be cutting a thread with sharp points.  However, at 200rpm, and taking 50 cuts to reach the full depth, and using a very sharp tool, the end result was OK.  I will fill the tearouts.

In order to make a functional join in the wooden cannon, I truncated the apex of the thread.  In the gunmetal version I will attempt a more faithful to the original, sharp look.

For some reason, the wood held together better during the internal thread cutting than the external.

 

The male thread was cut on my newly CNC converted lathe,  between centres, but the fixed steady on that lathe was just too small to hold the barrel, so the internal thread was cut on my bigger Chinese lathe.

Next I will bore the barrel to 63mm, then turn the exterior of the barrel.

 

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