Model Engine Maker
Supporting => Tooling & Machines => Topic started by: 90LX_Notch on December 07, 2014, 04:35:53 AM
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I needed an internal 10-32 Left Hand thread .500 deep on a part. 10-32 threads use a #21 (.159 dia) tap drill. I didn't want to buy a tap so I decided to "role the dice" and single point them.
I chucked up a piece .250 diameter O1 and set the compound at 30 degrees and turned one half of the form.
The compound was then set 30 degrees to the left and the second half of the form was turned.
This left me with a sixty degree "disk" that measured .146 in diameter.
A reduced section (shank) that measured .100 was then turned for .600 in length.
The part was then heat treated and tempered.
Next the 60 degree form was ground to the centerline (.073). This provides the cutting edge.
The bottom surface parallel to the cutting edge was ground until it "kissed" the .100 dia. shank. This provides the front clearance.
The back surface was also ground until it "kissed" the .100 shank. This provided extra clearance for navigating the .159 dia hole of the part to be threaded.
The cutting edge was honed with an oil stone.
I crossed my fingers and gave it a try.
Picture 1 shows the geometry.
Picture 2 shows the size of the tool.
Picture 3 shows the completed internal thread.
Picture 4 shows the mating part(s).
Picture 5 shows the parts assembled.
-Bob
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Hi Bob,
Nice work! Nothing like jumping in the deep end! Have seen quite a few articles on single point threading, don't remember anybody doing one this small. Would there be any chance of another few photos showing the tool from the end etc so we can see the shape you ended up with? I've got an internal thread coming up but it's a bit, well ok 52 mm, larger so can use a threading tool.
Cheers Kerrin
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Great work! There's not many folks who want to tackle internal threading, especially this small.
gbritnell
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Very impressive. Did you cut a relief groove at the bottom and thread left to right?
Also wondering why you needed a LH thread.
I recently acquired a thread mill that can do 8-32 and 10-32 threads, but haven't tried it out yet.
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I have thought about trying internal threads, but nothing so small. That is impressive and inspirational.
I have also considered making my own tap by cutting flutes on the sides of a screw. It might also require grinding or turning a taper on the end, and making some relief for the cutting edges, which is probably the most difficult part. It would also need to be hardened and annealed as needed, especially if it is to be used on hard materials such as steel. I haven't seen much about doing this but here is a little video of how to make a tap for cleaning existing threads:
http://www.etrailer.com/tv-FAQ-Make-your-own-thread-tap.aspx
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Kerrin- Thank you. More pictures are fourthcoming as soon as the batteries recharge for the camera.
George- Thank you very much.
kvom- Thank you. I used the threading tool to cut the relief groove. Yes, I threaded left to right. A left hand thread was needed because it's for the spindle of my New Hermes Engravograph engraver. I recently picked it up at a yard sale and the cutter was rusted in the spindle. The original Cutter Knob was damaged along with the threads in the spindle. The plan is to press this "insert" into the spindle after I bore the damaged threads out. The two threaded knobs in picture 4 above are Cutter Knobs that I made. They hold a .125 dia x 4.000 inch cutter and are threaded into the spindle from the top.
Paul- Thank you. I don't know if the carbon content of a screw would allow for it to be hardened.
-Bob
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Here is a more detailed description of home shop tap-making:
http://www.alloyavenue.com/vb/showthread.php?3033-Making-a-Tap-%28picture-intensive%29
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Bob,
Way back in tech school I had to make a turned test piece. Acme on one end (measured by wires) and the nut to fit. I think it was 1 or 3/4 inch, and standard thread on the other end. I don't think I would want to try 10-32. Although you should be able to thread outwards, I suppose that would make it easier. I did at work once do an odd thread and couldn't disengage once I started. Good job!
Art
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Art- Thanks. Yes, I had to hit the number on the threading dial perfectly because I was threading outwards. Hit it wrong, and it was all over because once the half nuts were thrown, it was threading.
Kerrin- Here are the pictures of the tool from different views.
-Bob
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Just checked McMaster to find that the 10-32 LH tap is listed at $5.95. I probably would have gone that way myself.
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Hi Bob,
Many thanks for the photos, helps a lot! Filed away for future use.
Cheers Kerrin
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I think you just lifted the bar Bob, well done.
Jim
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Just been checking the prices here, 10 32 LH tap by Goliath $NZ 34.20, might be tempted to single point a thread if I needed one, the smallest I'v done is 5/16" BSF, strangely enough, for the local engineering shop who said they couldn't do it(probably couldn't be bothered), but it got their compressor going again.
Ian S C
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Bob
I'm impressed! When I saw your tiny parts at CF last year, I was amazed. Now this. Great stuff.
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Jim- Thank you. I didn't raise the bar. I figured it was worth a try.
Ian- That's funny; the first internal single point thread that I ever cut was 5/16-32. That's where I came up with 60 degree circular disk for the first time. Armstrong use to sell a threading tool that used a disk; that's where i got the idea from.
Stan- Thank you. Not really all that amazing since the micro one didn't work when I completed it in May or June. I know where the problem is. I just haven't had the drive to redo what needs to be done for a while now. It's nerve racking at that size with an Atlas 618.