How should I go about cutting a 16mm x 1.5 mm trapezoidal internal thread?

[nickle]

I am working up to converting my x2 milling machine to cnc and am keen to use a spare mini lathe leadscrew to actuate the z axis. I would like to use bronze for th new nut .

Is cutting this thread a possibility?

Bear in mind the fact that thus far I have avoided single point threading on the lathe but I can work up to is one if need be. There is no tearing hurry.

I've considered making a tap from a portion of the leadscrew but will it survive cutting bronze?

Which way is likely to yield results for a novice machinist or am I better off chickening out and buying a ballscrews and nut.

Cheers,

Nick

[tekfab]

Whooo, definitely one to be discussed while sitting with some mates having a beer,  "Making v Buying"  always an interesting topic. I can see arguments for both but lets see what develops,

Mike

PS Learn to make it  ;-) 

[John Stevenson]

1.5mm pitch is very fine for the Z axis on a mill, basically 0.75mm across the flanks and not very deep.

A good candidate for premature wear.

[nickle]

I'm reluctant to buy but I'm pretty daunted by this one. I figured if any group could talk me through it it would be the mad modders

I wouldn't have posted if I didn't hold out some hope making the component myself though.

Nice point on the size of the threads... Would making a longer nut to spread the load across more threads help that or would I just be increasing the friction?


Cheers

Nick

[sparky961]

For what it's worth, I've successfully cut internal trapezoidal threads, something like 20mm x 4 in aluminum.  Bronze would be more difficult but not by much, I'd think.  As long as you have a lathe that can thread at the correct pitch, you should be able to get it done.

I ground a tool (similar to a boring bar) to the right shape, using the actual threads as a check gauge.  Only make the tool and thread as long as you need, as overhang will kill you here.  You may get away with plunging straight in, but better would be to go in at an angle or alternate which side of the thread you're cutting on each pass... but that gets tricky.

My advice is to take all of the advice you receive, then try it using any adjustments for your own situation.  You might break or scrap some tools, but you never further your skills in machining without both of the two.  Just make sure you learn from your mistakes. ;)

[andyf]

You might consider acetal instead of bronze, and try this:
< http://bbs.homeshopmachinist.net/threads/43645-Making-Acetal-leadscrew-nuts-the-easy-way > .

I hasten to add that I've never done it, but as a method it seems to have its devotees. Backlash is reported to be nothing to very little, but an old leadscrew might be more worn at what was the chuck end than towards the tailstock. But you would be no worse off with Delrin than with bronze, from that point of view.

Caveat: would Delrin be strong enough, on a fairly fine thread, to support the weight on the Z axis?

Andy

[BillTodd]

An alternative...

wktodd.webspace.virginmedia.com/drillmill/page2.html


Bill

[nickle]

I guess that would get me out of the internal threading! Looks like it comes with its own set of challenges though. I'll have to have a good look at your site to figure out how the device works. I was planning on rotating the nut rather than the screw so this option would be pretty spectacular in action.

With regard to the tool for internal threading would grinding a piece of 1/8 square tool steel to shape and then securing it through a round boring bar type tool be the way to go?

[sparky961]

With regard to the tool for internal threading would grinding a piece of 1/8 square tool steel to shape and then securing it through a round boring bar type tool be the way to go?

Yes, that's pretty much it.  Or, forge the end of a piece of drill rod (silver steel), grind, harden and temper.  Finally, you could also braze the piece of HSS or a piece of carbide to a round rod for the same effect.  Make sure you have good relief and the proper rake angle for the material you're cutting.  Google it.

I can't stress enough that you only want to make it as long as you need, but remember that you need a bit of stopping room when threading so you don't crash anything.