threading delrin - alternative method

I'm enjoying myself machining Acetal / Delrin and a tiny bit of peek.

Great for beginners and now that I have some non-ferrous inserts very satisfying.

so..I've machined my delrin to size, I want to create an internal 1/2"-20 thread - inexperience / low confidence strikes. I know that I'm running before I can walk,

I only need to thread 18mm deep -12 threads..and although I've gone to the trouble of setting up my change gear...so my thinking. And this is a long slow way.

To get the job done as the material is so easy to score...wouldn't it be easier to manually put 12 revolutions on the chuck...bring the tool out 0.3 cut on the way back..ect?

It's not powered threading but I get the opportunity to learn in slow motion?

Hi Steven,

I assume you place the cutting tool upside down and cut while rotating in reverse? A starting groove is a good idea. Rotating the chuck manually should work, many make a handle to put in the lathe mandrel, one example here (for ML10).

Thor

Edited By Thor 🇳🇴 on 16/05/2022 14:41:41

At 1/2"-20 and your interests I take it that it's to cap off a threaded muzzle or part of an actual moderator? If for a mod end connection I experimented with it some years ago and found it was a bit too soft thread wise for keeping everything square. Didn't take much to move it a touch altering the POI all the time or worse, clipping Defeated the object of having the minimum exit hole, for maximum efficiency, didn't have to knock it, just carrying about in a gunbag was enough, a decent AIM one as well.

A bed stop to show you how much further the lathe saddle needs to go before you reach the end is a great help on any sort of blind hole job.

Whether quick'n dirty "something" clamped to the bed [toolmakers clamp perhaps], nicer micrometer adjustable version, full monty multi-position turret stop or uber sophisticated single tooth dog clutch variety that drops the feed when you get to the preset end-stop. I have the lot, albeit my something clamped to the bed is more engineered than quick'n dirty, and all have their place. When you work up to your "forever lathe", or at least "keep a long time lathe" I'd strongly advise investigating how to get one of Graham Meeks single tooth clutch systems fitted. So much less stressful. But thats for a year or six in the future.

+1 for the mandrel handle suggestion from Thor. With only 12 turns to do its likely to be quicker than neophyte level stepping through screw-cutting procedures and you can stop instantly when you have that panic brain turns to mush "aargh what do I do now. I've cocked up and wrecked it." moment.

Anyone who claims to have done significant screw cutting yet not had that panic moment is flat out lying.

Big time.

Fortunately you generally get away with it. Well I did, severally.

When it comes to forward and reverse running its well worth spending a bit of time and experimentation to make clear to yourself the difference between setting up for a left hand thread and cutting a right hand (normal) thread running in reverse. No need to cut anything pencil as a tool, paper wrapped round a mandrel as the work piece.

Clive

+2

Remember to remove it when you're done!

Edited By Peter Greene 🇨🇦 on 16/05/2022 19:08:07

Winding in reverse but with the tool the right way up but at the far side works as well. Then with a bigger thread you can see what's going on. I usually cut internal going the right way (my last lathe had a screw on chuck) but with the tool inverted at the far side, then feeds were the same as external, and the chips fall away from the tool

Thanks for the speedy replies.

Thor- I like the mandrel idea, quite simple.

Reversing the tool? Doh! - the tool only cuts in one direction.

Bezzer - yes, its a conversion to a poorly fitting slip-on moderator. Good mod just a bit chewed up.

Plan is to fit a washer in the shoulder to tighten up against and hopefully stop the end cap from distorting on a narrow contact area.

Clive- Pencil and paper..too damned simple

As the workpiece is internal- what I was planning to do is have a dry run/ pitch check on a piece of PVC conduit. Won't damage the carbide and gives a good visual.

I have a feeling that this will pare off in a single spiral, will find out as I go.

All in the learning curve.

+1 for the mandrel handle but I would not attempt to cut in both directions due to backlash in the leadscrew (plus my chuck screws on so it might screw off). I always back the tool away from the cut when running in reverse - powered or otherwise.

FWIW I sometimes use power just on the reverse (non cutting) direction... provided that the mandrel handle is removed each time!

Came up with a technical issue - with the 8mm (min 11m i/d) indexable boring bar and for that matter the screw cutting tool.

The tool-post is too low to put the tools in the centre of the workpice, messed about making shims to get the tool to the top of the post and was still about a mil out.

Shims under the tool post?

Yep. Shim or thin spacer under the toolpost is perfectly acceptable.

Aluminium alloy if you have it because steel on aluminium alloy is grippier than steel on cast iron or steel.

My P&W lathe has a shim under its Dickson QC post to equalise the set height of the tools with my Smart & Bown. So I can simply share tooling rather than having two sets, one for each lathe.

Clive

To make perfect-fitting feed screw nuts, the “heat’’n’squeeze” method works well.

Might this method be suitable for this application?

Searched ...ah yes backlash.all round.appears to be part of the 210s specs.

I have some aluminium -

Yesterday I turned the shed upside down looking for a bag od 50x75x1.5 mm aluminium strips, unable to find those ..I cut and ground flat some 3mm & 5mm plate.

Today I found the aluminium ...it wasn't in the shed.

Sorry. Don’t see any connection to my suggestion.🙁. Please explain….

apologies, new forum- different format, should have been a multi-quote, aluminium waffle was directed at Clive.

Not allowed to right click copy and paste.to start with

I guessed you meant something to do with half-nuts ( I'm learning quickly) but otherwise had no idea of what you were on about,until I searched the forum.

I honestly don't believe there is part of this machine without some level of backlash..that wouldn't need some kind of skills and experience currently beyond me or perhaps even warranty voiding modifications.

.I'm very doubtful of the boxes ticked and tolerances quoted by QC although with time and patience I will get closer to them.