A big ol' chunk of delrin

Let us know how it goes. I first heard of heat forming Delrin nuts right here on this group years ago. For my application I went with a spring loaded anti backlash Delrin nut from DumpsterCNC back then instead. I don't think DumpsterCNC is still around.

This is interesting , your text did not show up in the post over on e-s but it did here on blocknews ...

Now to the meat of the sammich . I have been out in the shop all morning making a tap* to match - pretty closely - the leadscrew on the mill . The plan as of right now is to tap the hole I have made in a chunk of that delrin . I'm hoping for a tight fit so I can heat the leadscrew to finish forming the threads without splitting the nut . If it's loose I'll slice the nut in half and heat/clamp to finish forming the threads . If it's too tight to thread on I can split one side to get it on the leadscrew and heat form from there . *I still have to form the flutes on that tap . I'm thinking a 1/2 or

shop break

Well , the tap idea isn't going to work , I guess I'll stop and rethink my approach . But at least I was outta my wife's hair for the whole morning !

This is interesting , your text did not show up in the post over on e-s but it did here on blocknews ...

Now to the meat of the sammich . I have been out in the shop all morning making a tap* to match - pretty closely - the leadscrew on the mill . The plan as of right now is to tap the hole I have made in a chunk of that delrin . I'm hoping for a tight fit so I can heat the leadscrew to finish forming the threads without splitting the nut . If it's loose I'll slice the nut in half and heat/clamp to finish forming the threads . If it's too tight to thread on I can split one side to get it on the leadscrew and heat form from there . *I still have to form the flutes on that tap . I'm thinking a 1/2 or

shop break

Well , the tap idea isn't going to work , I guess I'll stop and rethink my approach . But at least I was outta my wife's hair for the whole morning !

I did see Bob's post on E-S.

For a single use tap you could flute it with one corner of a square ended endmill, perhaps one with dull corners that you beveled sharp again, using your endmill fixture at the back relief instead of the cutting edge angle. If a hard spot in the rebar dulls it you can regrind it the same way. It's my go-to endmill for roughing steel of uncertain parentage and upbringing.

A tap drill size pilot plug on the tap may help keep it centered and straight.

In aluminum at least unhardened steel dulls quickly.

I will soon try making a tool from a scrap of broken rock drill pipe, and see how easy to saw and turn it is.

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I'm thinking at this point that I might try threading the inside with a boring bar and a cutter that is close but narrower than the groove width of the thread . This will make it necessary to split the nut and hot form the thread . My main concern about splitting the nut is whether the halves will fuse together into a solid unit during the forming process . I'm once more stepping off into unknown territory ... but you know what they say "keeping learning will keep you young" .

I'm thinking at this point that I might try threading the inside with a boring bar and a cutter that is close but narrower than the groove width of the thread . This will make it necessary to split the nut and hot form the thread . My main concern about splitting the nut is whether the halves will fuse together into a solid unit during the forming process . I'm once more stepping off into unknown territory ... but you know what they say "keeping learning will keep you young" .

Don't be a wuss -chuck it in the 4 jaw and single point it. If you grind your tool right you won't even need to heat form it - - - -

The problem with that is that I'm not certain what the thread profile is - probably acme but ... I was just thinking that I can make an impression of the leadscrew , wax might work or clean the leadscrew well and apply a release compound and mold one out of JB weld ... and use that impression to grind a cutter . That piece of plastic is dialed in on my 4 jaw , and ain't coming out just yet .

From the discussion, I'd guess that it may be a ISO Trapezoidal thread, specifically TR24x3.

.

Otherwise, it's likely an Imperial Acme thread, 8 TPI.

Measure the thread pitch to tell. 3mm pitch is 8.47 TPI, a ratio of

Joe

I actually made a second post talking about creating a makeshift tap from a piece of the the same acme or trapezoidal thread. It never showed up. I only post through ES these days, but I do read the group when I'm out of the office on narkive.

Making a single point tool, as others have mentioned, is an option, but a form tool that large can cause chatter, deflection, and other issues. An option is of course a narrower form tool. Cut the thread, and then offset the tool until you get the width you need.

In any case you already have a gage you can use to make the form tool.

Internal single point can be tricky, but your tool bit can be short and held in an old school shop made boring bar. Cross drill for the tool bit. Drill and tap the end for a grub screw.

I realize you already have Delrin, but brass or bronze pinch nuts can make decent reduced backlash lead screw nuts. Particularly bronze. Typically three screws. Two pulling it together and one pushing it apart. At the same time you can drill and tap for an oil line. A fairly sloppy nut can be adjust to less than one thousandth backlash. My very first mill, the Taig CNC mill, used "precision" v-leads and pinch nuts on all 3 axis. I could dial in to about a half thousandth backlash for precision work, or let it flop around at about 3 thousandths for faster running without losing steps on the motors. I did have to decide what good enough was for the various capabilities.

My second CNC mill, (The Max NC 5) also used pinch bnut son V-leads, btu I changed it to spring loaded DumpsterCNC nuts on acme screws for X/Y and a ball screw on Z.

If you single point I think you can hand grind more than accurately enough to cut your nut if you don't have other options, but I seem to recall you do have some real tool grinding capability.

The problem with that is that I'm not certain what the thread profile is - probably acme but ... I was just thinking that I can make an impression of the leadscrew , wax might work or clean the leadscrew well and apply a release compound and mold one out of JB weld ... and use that impression to grind a cutter . That piece of plastic is dialed in on my 4 jaw , and ain't coming out just yet .

-- Snag

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An old way was to fit a piece of thin sheet metal into the leadscrew grooves, holding them up to the light to see gaps to remove, like restoring a wood chisel or plane blade with a square. Another was to press sheet lead into the thread or gear teeth. When you have a light-tight match you measure the angle and grind the bit to it, perhaps narrower so you can adjust the depth and width separately to fit. I made a fly cutter to mill an ANSI involute spline broach by cut and try.

Polymer clay works well to copy shapes, such as your partly cut thread. It hardens when moderately heated and can be cut into a flat template. I didn't find a cheaper lubricant-filled alternative to Moglice, Rulon etc. though some suggested JB Weld.

From the discussion, I'd guess that it may be a ISO Trapezoidal thread, specifically TR24x3.

.

Yes, but a little bit of wear will erase the distinction.

Joe

It's definitely an 8 TPI leadscrew , moves the table .125"/revolution plus/minus a few tenths . OD is within a few thousandths of 15/16" . Tell me more about this imperial acme thread ... this machine is a copy of the RF45 , made in China in 2001 . I got it new IIRC in '02 or '03 . I've made a lot of stuff with this machine .

Yes, but a little bit of wear will erase the distinction.

Joe

----------------------------------- I'd like all my mistakes to be accidental.

"An old way was to fit a piece of thin sheet metal into the leadscrew grooves. Another was to press sheet lead into the thread or gear teeth."

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A lead ball and a c-clamp shall solve the question of thread profile . I have angle gauges I can set up in the mill vise to get the proper angle on the cutter using my end mill sharpening grinding disk .

It's definitely an 8 TPI leadscrew , moves the table .125"/revolution plus/minus a few tenths . OD is within a few thousandths of 15/16" . Tell me more about this imperial acme thread ... this machine is a copy of the RF45 , made in China in 2001 . I got it new IIRC in '02 or '03 . I've made a lot of stuff with this machine .

-- Snag

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I used two import mills with 8 TPI leadscrews and slowly learned to adapt to counting 125. 250 375 500 625 750 875 1000, then adding the dial reading. Had they been mine I would have tried hard to convert to 10 TPI, even if it meant 3/4-10 all-thread like I used to repair my surface grinder.

In WW2 US firms took on production of the Merlin engine and Bofors autocannon, and found that both had been designed with loose tolerances that required expert hand fitting.

A mechanical engineer I knew had converted John Browning's dimensions for the .50 BMG from 128ths of an inch to decimals.

In the US, Imperial (meaning inch) Acme is better known as ANSI Acme, as documented in Machinery's Handbook. The biggest standard ANSI Acme is 5/8-8 Acme, which is only 5/8" in diameter, not 15/16", so we may have a franken-thread here.

Cutting one thread or the other into the same size leadscrew blanks would make production sense.

The cleanest way to tell is to measure the pitch diameter with three identical number-drill blanks and a micrometer on some unworn area (so the flanks are good).

.

Joe

PS: It may have been Ox Tools who did a video on melting delrin to make a new nut to fit an existing leadscrew. JG

I did just that once I figured out the thread was acme ... even made a fixture to get the angle correct because I'm not as accurate freehand as I felt this project needed . Next time I need to make an acme cutter it'll be easy .

I will soon try making a tool from a scrap of broken rock drill pipe, and see how easy to saw and turn it is.

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It wears an HSS bit dull in a few minutes unless the lathe is in back gear. Annealing or tempering in the wood stove to at least 600F when I removed it from the tin can after the fire died down seems to have helped tool bit life.