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. I read every comment and respond to most. n.b. There is a list of my first 800 posts in my post of 17 June 2021, titled "800 Posts"

Tag: Model Engineer

December 27, 2016

Reversing Gears and Handwheel

Another 2 days in the workshop.  Heaven.

I had made a worm drive and gear using an M14 x 2 tap, but it did not look the part, despite being functional.   The problem was that the threads were sharp triangular and they did not look correct.

So I made a worm drive and gear using Acme specifications.  The teeth have a chunkier squarish look.  More authentic.

I ground a lathe cutter and used it to make the worm drive in gunmetal, and another identical thread in 14mm silver steel (drill rod).   The steel thread had cutting edges formed, and when finished it was hardened by heating red hot and quenching.  After hardening, a file would not mark it.  I did not bother to anneal it, since it would be used only to cut cut brass or gunmetal.  The hardened tool was used to make a gear in gunmetal.  Unfortunately I did not take pictures of those steps.

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Showing the handwheel, worm drive and gear.  the shaft is mounted in gunmetal bearings which are bolted to the columns with BA8 bolts.    The thread is Acme. 2mm pitch.  The handwheel will control forward-reverse of the triple expansion steam engine.

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In order to determine the position of the bearing bolt holes for the worm drive, I used SuperGlue to tempararily join the worm and gear.  

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When the position of the bearings was determined, the holes were drilled 1.8mm and tapped.  the taps were BA8, about 2mm diameter.  The engine is held vertically on the milling table, being cramped to a large angle plate.  The holes were drilled accurately on the mill.  The threads were made using a tapping head made by me from plans published in “Model Engineer” by Mogens Kilde.   The double parallelogram of the tapping tool keeps the tap vertical.  The tap did not break.

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Close up photo of tapping the BA8 threads.  Showing the bearing, shaft, worm drive and gear.  Note the Acme thread.  The bearing is Super Glued into position to facilitate the drilling and tapping procedure.  The Super Glue will be removed later.

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The final step for today was to make the handwheel.  It is 1.5″ diameter.  The rim is 1/8″ brass and the spokes are 1/16″ brass.  I made 4 of these, with each being better than the last.  I softened the 1/8th brass before winding it around a 32mm pipe to form the rim.  The join in the rim was silver soldered.  Then the rim and the hub were drilled using a tilting indexing head on the mill.  I soft soldered the spokes on intital handwheels, but the final (and best) examples were glued with Loctite.  Loctite allows a few minutes for adjustment of the spoke lengths, whereas there is only one go with the soldering.

It is looking interesting, Yes?  And there are 3 spare handwheels.  The rest of the reversing mechanism components were made several months ago.  Almost ready to install them.

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January 17, 2016

TAPPING GUIDE

I took another break from the triple to make this tapping guide…

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The tapping guide in use.  BA7. (staged photo)

 

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CNC drilling and reaming

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CNC milling the flanges

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The completed arms and flanges

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Milling the jaws manually

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The jaws in position

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Showing the jaws holding a tap. The jaw cover is removed.  The  hole in the side of the chuck is for the M5 grub screw which opens and closes the jaws.

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Showing the jaws cover in place.

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The 3 jaw chuck provides a convenient and accurate base. Alternatively, the guide could be supported in a hole in the bench.

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Very handy for tapping threads in items not readily held in a vise.

The biggest problem with tapping threaded holes is taps which break in a job.  Sometimes after many, many hours making a part.   Sometimes the broken tap is able to be removed, and sometimes it cannot, resulting in a ruined part, wasted time and much wailing and gnashing of dentures.

Keeping the tap vertical at all times during the tapping procedure, and using a sharp tap, suitable lubricant, and appropriate torque, are the keys to not breaking taps and saving teeth.

Usually I do my tapping with the tap held under a spring loaded guide in the chuck of the drill press or mill, and the workpiece in the vise.  This method prevents any inadvertent bending of the tap, which avoids one of the major causes of breakages.

But sometimes it is just not possible to hold the workpiece in the mill or drill press and the tapping has to be done freehand, aligning the tap by eye.  I am rarely satisfied that the tap is vertical after using this method.  Lack of accuracy, and higher chance of a broken tap is the consequence.

So when I saw this tapping guide in “Model Engineer”, and saw the possibilities for its accuracy and versatility, I decided to make one.  The fact that much of the machining could be CNC’d was an added attraction.   Also the 4 jaw chuck was intriguing.  I had seen one made by a colleague in the Melbourne Model Engineering Club, and I was keen to see if I could manage it.

The design was by Mogens Kilde and the plans were published in the August 2015 “Model Engineer”.    I made a few minor changes to the design, mainly using thicker aluminium in the arms and flanges.  I used stainless steel for the chuck body because that was the only free machining steel which I had in the size.  I used key steel for the chuck jaws, again because that was what I had available in my workshop.

The double parallelogram arms keep the tap vertical within the limits of the arm movements.  Using a 3 jaw chuck as the base of the unit provides a lot of flexibility in positioning the guide.

I will not comment on the actual building, because that is clearly explained in detail in the original ME articles.

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