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Tag: ebay

Next Tool Project…A CNC Laser Cutter

The Southworth steam powered boiler feed pump has many gaskets.  I have not counted them, but there must be 15-20.  All with many 2mm and 4mm  holes.

And in the process of making the machine, I have broken quite a few of them with the multiple assemblies and tear downs.

But, fortunately, 2 of the members of my model engineering club have laser CNC cutters, so extra sets of gaskets has not been an impossible ask.  (Thank you Brendan and Stuart!)

So, some time ago I asked Stuart, if it would be possible to attach a laser cutter to the CNC mill.  His initial answer was NO.  But recently, he changed his tune.   He attached a laser head to his 3D printed CNC mill and started producing gaskets on request!   So, as is a recent pattern, I am walking in Stuart’s footsteps, and I have purchased a 15 watt laser head on Ebay.   Chinese of course.

Laser kit 15w

This is the kit.   Cost $AuD146.

Laser head

And this is the 15w laser head.  Now I have to work out how to attach it to my mill.  Shouldn’t be too difficult, as long as I don’t turn on the spindle while it is attached.

 

P1032882

My CNC mill, during the electronics upgrade.  Most recent photo.   Soon to have a laser head.

Stuart assures me that Mach3 can be configured to operate the laser….   turn it on and off, move the axes at an appropriate speed, etc.  I think that some trickery is involved.

And future gaskets will be as simple as ….

So watch this space .

CNC lathe conversion-6. EBay problem

My first hitch occurred today.

I was very excited to receive the nut for the cross slide ball screw.  If you have been following these posts you might recall that the ground ball screw for the cross slide came from Taiwan, and arrived in 3 days.  But I had to order the nut from a seller in USA.  The nut was advertised as new old stock, but with no packaging.  That was OK, but the postage cost for such a tiny item was ferocious.

It was the last item to arrive from overseas.   However when I looked at it, it was obviously NOT new.

IMG_4043.JPG

The cap screws holding the ball recirculating tube were different from each other, and the washers underneath were too big for the screws.  Obviously not the way that TNK made it.  Somebody has had the nut apart.  And the ball retaining tube was very scratched  and loose.  Again, not TNK standard.

But no biggie.  If it works — fine.

So I turned up a retaining tube to remove the previous nut from the ballscrew, and it came off without any drama.

cnc lathe - 1

But when I tried to fit the “new” nut, it just would not go on.  Tried reversing the direction.  No go.  Bugger bugger.

Somebody has altered or changed the “new” nut.  Maybe installed balls which are too big, or maybe damaged the entry thread.  I do not know.

What to do.  I have been waiting 2 weeks for this to arrive.

First, Ebay email to the seller.  See what the response is.  Ask for a refund.  The postage was almost as expensive as the nut. If unsatisfactory response, they will get the worst Ebay feedback ever.

There is one other seller of these nuts on Ebay, also in USA, and 50% more expensive, and the postage is also 50% more expensive. (how DOES ebay come up with the postage charges.  It seems more related to the cost of the item rather than the weight-size etc.)  But the nuts are in original packaging.  And I want to get going with this, so fuck it.  Pay up and get it.

I will report in a later post.  (if the bad language in this post seems to reflect my state of mind, well, yes it does.)

 

PS.  Next day.  After sending photos of the issue, the seller accepted responsibility, and I am getting a full refund.  That restores my faith in Ebay/Paypal.   I hope that the next one is in better condition, and comes a bit more quickly.  Sorry for the bad language.

Ball Screws -2

This is a brief post to give a 10/10 rating to an Ebay seller with whom I have had dealings recently.

I have bought 2 ball screws and ball screw covers and ball screw bearings in 3 separate transactions from a supplier in South Korea.

Postage was included in the “buy it now” price.  In one case I offered a lower price, which was accepted within minutes.

After paying by Paypal, I received confirmation within an hour in each case, that the item had been shipped (actually air freight by Fed Ex).

In each case the items were delivered to my door in Australia within 3 days!  (it takes 5 days to get a parcel posted from Melbourne to Geelong, a distance of 65km).

And in each parcel there was a very nicely handwritten card thanking me for the purchase, and promising support if there were any issues with the items.

One ball screw was brand new, repackaged as advertised.  The other was used, salvaged from used machinery, but in “as new” condition.   Both were C5 grade, which is normally stratospherically expensive and has to be specially ordered.  They were priced only slightly higher than new rolled (lower grade) ball screws.

They were very carefully packaged in heavy duty cardboard rolls with metal ends, and multiple layers of heavy plastic and foam sheeting.

I made a later purchase which involved the seller removing a part from a machine.  He added it to a parcel which I had also ordered and wrote that I could pay later for the part if I was satisfied with it.  The price for the part (a THK bearing) was $UAUD32.  The same part new here would cost $AUD400.

In every case, communications have been  answered within a few hours, polite, personalised and in excellent English.

My only complaint, and it probably relates to the shipping arrangements, is that there appears to be a size restriction on shipping to Australia, of about 1200mm.  (p.s.  apparently the “do not ship to Australia” are old adverts, and there are no restrictions now.  A message to dy-global is all that is required to get any item shipped).

I hope to deal again with this company.  The name is dy-global.  To find them you need to search Ebay USA, or use the international settings on Ebay Australia.

Lathe conversion to CNC -3 Ball Screws

I have learnt a lot about ball screws in the past few days.  And I have purchased 2 ball screws and nuts on Ebay.  For those relatives and friends who follow this post, who have no idea what I am talking about, the “ballscrews” are what determines where the cutting tool on the lathe is positioned.  Very crucial.  (can something be “very” crucial?  It looks a bit like “very unique”. )

1

Ball screws are the usual positioning screws  for CNC machines these days.  The alternative is Acme or square thread screws, but the few manufacturers who used to use these have all switched to ball screws (as far as I know).  Even Wabeco, the respected German lathe manufacturer no longer specifies any threads except ball screws.

Ball screws require less power to turn due to friction being a fraction of the alternatives.  Ball screws are silent.  If they are noisy there is something wrong.  They are generally more accurate than square or Acme threads.  They used to be many times more expensive than the older types, but since China/Taiwan has taken over most of the manufacturing, often using equipment sourced from US/Europe/Japan, the costs have plummeted.

And the backlash is minimal or zero.   Another name for ballscrews is “antibacklash screws”.

Backlash is annoying on a manual lathe, but it is very important on the cross slide of a CNC lathe.  Interestingly, it is less important on the CNC lathe lead screw, because most CNC lathe machining  on the leadscrew occurs in one direction only, towards the headstock.  However,  the cross slide is machining in both directions, in and out,  so the absence of backlash is necessary to maintain workpiece accuracy.

Ballscrews have grades of accuracy varying from C0 -C20.  The bigger the number, the less accurate the screw.   In general, it is recommended that industrial lathes should be C3-C5,  which means zero backlash, and accuracy of about 0.001mm.  That degree of accuracy is quite expensive, costing thousands of dollars per screw, and only attainable in ball screws which have been finished with precision grinding.  The alternative is ball screws which have been “rolled”.  These are much less expensive, costing hundreds of dollars per screw, depending on the degree of accuracy.  The best rolled screws can attain an accuracy of 0.01-0.02mm (C7), down to 0.1mm (C20).  These are approximate figures which I have gleaned from several manufacturers’ specifications.

So from scale drawings of the lathe bed and carriage and cross slide, I worked out that I needed the following…

 

IMG_3978.JPG

This is a photo of a ball nut and screw very similar to what I have bought for the cross slide.  THK brand, 14mm diameter screw, 4mm pitch, and BNT nut style.  Note the rounded channels that the balls occupy.

 

  1. Cross slide screw 14mm diameter, 400mm long with at least 200mm of thread, and a thread pitch of no more than 5mm.  The cross slide nut needed to be a THK BNT pattern in order to fit into the cross slide with a minimum of space making machining.  THK is a large manufacturer, with intermediate prices, and a very good reputation.  The screw needs to be a specific length, and one end needs to be machined to go through a bearing/ bearing housing and have a tooth belt pulley attached.  I contacted a ball screw supplier, to enquire about ground ball screws, but discovered that these were rarely specified due to their cost, and delay of 3-6 months.  A C7 rolled screw with the BNT nut was going to cost about $AUD400-450.  So I searched Ebay Australia, Ebay USA, and Ebay UK.  Eventually, I found and bought a used ground screw with end bearings and housings from Taiwan for $AUD250.  The nut was the wrong type, but I found a new correct style nut on Ebay USA for $AUD100.  I know that sounds like I have not saved much money, but that gives me a super-accurate ground ball screw!  Of the correct size and type.  I am keeping my fingers crossed that the pieces sourced from different countries will go together.  Theoretically, they should.  (same manufacturer, same size, “ground” specification, etc etc.  but finger tightly crossed).
  2. The lead screw approximately 1000-1100mm long, 25-32mm diameter, and 5-6mm lead.  Super accuracy not required in the lead screw, and I could have bought a new rolled one from China for about $AUD300-400.  But then I spotted one in South Korea, new old stock, 28mm diameter, 6mm lead, with unmachined ends.  THK brand.   Asking price just within budget.    And this was a C5, ground screw, possibly more accurate than I expected for the price, and unused, but hey, it sounded like a bargain.   So I offered about 15% less and was somewhat surprised to have the offer accepted.   So that one is arriving in a week or two.  Then to buy mounts and arrange end machining of the screw.  Although not crucial it will have zero backlash, due to the C5 designation, and the fact that it has two ballnuts bolted together in a “pre-loaded” fashion.  I expect that it will be the most accurate component on the lathe!  No decent photo to post.

(ps.  see the comments section for discussion about axial accuracy and backlash.  A super accurate C5 ballscrew has axial play (backlash) specification of 0.020mm, but the double ballnut configuration will reduce that number substantially.  “zero backlash” apparently does not really mean zero.)

 

 

 

 

New (to me) Toolpost for the Colchester

I have been looking for a replacement tool post for the Colchester Master 2500.  The one which came with the lathe was broken, and it had only 2 tool holders.  Hmmm…  Surely I would have noticed that during my fairly detailed inspection.  Other small bits were missing from the pile of accessories on the pallet too.  I should have taken photos.  The photos on Ebay were distant and blurred.  (I wonder why….).   Buyer beware.

So I have been checking Ebay Australia.  Only Asian copies, and not cheap.

Ebay UK.  A few genuine Colchester tool posts on offer, but very expensive.

Ebay USA.  Again, a few on offer, and one in particular looked interesting.  A Dickson style tool post, with 6 tool holders.  Said to be suitable for a US version of the Colchester, but a larger lathe than mine.   So a quick question to the seller about postage costs (where does Ebay come up with their estimates?  The Ebay estimate was double what I finally paid) and the seller agreed to put the items in two  “Flat rate boxes”.  I paid his buy it now price.  I took a gamble on the apparent lathe size discrepancy, figuring that I could resell the items on Ebay Australia if they were totally unsuitable.

4 days later, the parcels arrived.  I have bought quite a few items from the US, and invariably the service has been fantastic and fast.  I do feel a bit guilty about the energy and pollution involved with buying tools from far off countries, but there is no viable local alternative.

IMG_2957

The tool post was exactly the correct size.  The exterior  had been cleaned up, but the workings required some freeing up.  The tool holders were the same size as the two I had already, so now there are 8 tool holders….   a goodly number.  The brand label had worn off, but it appears to be exactly the same as the original Colchester.

The final cost?   $US250, plus $US125 for postage.   All up about $AU500.  Pity about the exchange rate.

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