[cncbob]

I have a 5/8 - 10 all threaded acme rod. I need to cut a length approximately 12". I am going to use it as a lead screw on the cross slide on my lathe. The old screw had ends machined on it that were smaller than 5/8. I plan to machine the ends of the threaded rod down to match the ends of the old screw.

My question is how can I be sure that the threaded rod is turning true? Is there a way to use a dial indicatior on an acme screw thread?

Any guidance would be helpful.. THanks!

[GaryCorlew]

Most people just use a putty knife, they lay it in the threads and hold it then put the di on the putty knife and then just true it up. It would be best if you do it in a four jaw chuck.

[widgitmaster]

To keep the other end from going off center, cut a plastic knob with an OD slightly smaller than the spindle ID.

Or, hold it short in the chuck or collet, and center drill each end, then turn it between centers!

Have fun!

[cncbob]

Excellent tips guys!! Thanks for your expertise and willingness to share. I'll give it a try and keep you all posted.

Thanks!!

[cncbob]

Hello All!!

WOuld it be possible to make a tap out of a piece of Acme threaded rod? I have a piece of 4140 (I think) precision threaded rod that I am using for a leadscrew for a lathe cross-slide.

I need to machine some nuts to replace the worn ones. I have a piece of bearing bronze that I plan on machining the nuts out of. I am going to need to tap the holes in them to accept the leadscrew. I thought it may be worth my time to at least ask if I could make a tap out of the left-over threaded rod to tap the threads in the bronze. I have found some commercial taps, they are $$EXPENSIVE$$.

Is this just wishful thinking or is this feasible?

Thanks in advance!

[vger]

Yes, I did it with just a drill press, a file, and a 1/2" end mill. Just cut a 6" section of 1/2" acme, chucked it in the drill press, filed a taper down on it, then set it in the cross slide vice and carfully cut along the tapered length to one side to make the cutting edges. Just 2 flutes but... hey makes great acme nuts in delrin.

[Guldberg]

Deldrin yes, bronze, i doubt. I made a tap for trapezium screw tr16mm x 4mm, i just barely could make a nut from a piece of quite hard polymere. I tried it on brass, but didnt even get started

[NC Cams]

Grab it with a collet. This will both clamp to OD and hold it rather concentric.

YOu can machine up a concenteric bushing that will slip on the OD with minimal press and then pilot it with a three point steady rest/centering fixture.

The collet should hold it adequately to cut the OD down and/or center drill it and perhaps tap it as needed.

You can always thread a piece of nicely turned billet with either Acme or UNF or SAE threads. Classic case of the lathe fixing itself....

[gmac]

4140 is a hardenable alloy but it may be moderately hard already- check and see what stuff you have. after machining it into a tap form you may be able to harden it, and possibluy case-harden if necessary for the service you need. sounds like only one or two nuts to make so the hardened version should suffice. google up '4140 hardening' and see what the procedure is for your piece, there are about 41 thousand hits. running a basic acme or trapeziodal threadform at the same nominal pitch but at reduced diameter using the lathe to hold the nuts in the headstock and a boring arrangement to cut the thread should give you a good start and then use the acme tap you made to finsh the internal threadform off. this will give you a nut that is possibly closer to your actual screw dimensions than a manufactured item would be ( no tolerances figured into this cutting operation - it cuts the size of the rod, not the size that a typical manufactured tap would cut) so watch out for binding from this result. taper the entry to the threaded area on the nut and check out what lube to use for tapping the nut material and you should have no problem. as always- make sure the tap is stoned sharp after hardening and the edge area machined before hardening is not decarbonized when the hardening is done -grind back to the hard area and sharpen properly if this happens. if you are really particular, set up the leadscrew and gearing so that the nut chucked in the headstock advances into the tap held in the compound ( use a boring bar holder or other clamping arrangement) at the correct pitch. set up thus, you dont need the cross-slide advance to make this part, just the main leadscrew. watch out for tap hitting the chuck- use the reverse scenario ( with the nut on the cross-slide and tap held in headstock) if its more convenient, and you can thead by hand turning the chuck with a crank.