Tight Threads

[Robert111]

It always seems that the threads I make for the section/barrel and cap/finial are too tight. The triple lead threads for the cap/barrel are okay. I'm guessing that when I make a joint that unscrews in a couple turns, like the cap/barrel, no problem. But when I make a joint that has half a dozen turns, it's always too tight.

This is what I've done in an effort to cure this:
1. I cut away the male threads next to the shoulder down to the "minor" diameter (I think it's called). I cut away threads for a distance of maybe 3/32 from the shoulder.

2. I undersize the tenon for the male threads; for example, I make the tenon 9.6 mm for a 10 x 1 die.

3. I run the tap in a few times, and if the material and wall thickness will allow, I'll apply a little side pressure to make the female threads a little deeper and/or wider.

I've been wondering if adjusting the little screw in the dies might help.

All in all, this is costing me A LOT of time.

 

[mredburn]

Reverse the die after the initial threading and see if that helps. Some of the dies are tapered front to back and you need to reverse the die and run it on the threads again. I have had that problem with a couple of my dies that are imported. Some of those imported dies I have had to grind the face down to get threads all the way up to the shoulder. I generally only reduce the tenon by .2mm Or 9.8 for the 10m tenon.

 

[frank123]

Unless you are using a bottoming tap you may not be tapping deep enough and getting a tapered female thread that gets tighter the farther in you go.

Same can happen with the die, if there is no starting thread taper on the back side of the die turning it around and recutting the thread all the way to the end of the sized section will help in cutting the threads to full depth all the way.

Have you tried just a short (scrap) cylinder of the material you are using and drilling and threading it completely through to see if that makes a difference?

If you are working with a fairly flexible material it could be expanding when you tap it and contracting again after the tap is removed (particularly if you're using a cheap tap that isn't real precision and sharp) making the threaded hole undersized. Try threading a piece of aluminum or something similar to see it that makes a difference.

The problem may not be related to any of these things at all, they're just things I have run across in my limited experience.

 

[Robert111]

First, thanks Mike and Frank.

Reverse the die after the initial threading and see if that helps. Some of the dies are tapered front to back and you need to reverse the die and run it on the threads again. I have had that problem with a couple of my dies that are imported. Some of those imported dies I have had to grind the face down to get threads all the way up to the shoulder. I generally only reduce the tenon by .2mm Or 9.8 for the 10m tenon.

Yep, I'm reversing the dies every time I use them, Mike. And I too generally only reduce the tenon by .2mm for the male threading (to 9.8, for the example) but in an effort to find a cure for this problem, I'm trying everything. And I can't blame it on any particular t&d set, they all do it.

Unless you are using a bottoming tap you may not be tapping deep enough and getting a tapered female thread that gets tighter the farther in you go.

Yeah, I thought of that and have been running the tap in as far as the situation allows to get past the taper. That helps a little, but the problem persists. As I screw the pieces together, they screw pretty well at first, then after maybe 3 or 4 turns, they get tight, to the point that I cannot screw the male piece all the way in. That's when I start using my tap wrench and pushing to the side as I screw the tap in and out, gradually widening the joint so that the male piece willl screw all the way in.

Same can happen with the die, if there is no starting thread taper on the back side of the die turning it around and recutting the thread all the way to the end of the sized section will help in cutting the threads to full depth all the way.

Yep, I do that.

Have you tried just a short (scrap) cylinder of the material you are using and drilling and threading it completely through to see if that makes a difference?

Yes, same result--tight.

If you are working with a fairly flexible material it could be expanding when you tap it and contracting again after the tap is removed (particularly if you're using a cheap tap that isn't real precision and sharp) making the threaded hole undersized. Try threading a piece of aluminum or something similar to see it that makes a difference.

Well, I thought about the elasticity factor, and started changing my technique for using taps and dies. I turn the tap or die three quarters of a rotation in, then back it out two quarters. Then repeat until finished.

The problem may not be related to any of these things at all, they're just things I have run across in my limited experience.

 

[frank123]

You may have either a tap or die that is not cut to the exact thread pitch.

For example a 1 mm die thread would thread into a .98 mm tapped hole for several diameters before the mismatch took up all excess clearance and started binding. (not necessarily the real numbers, just an example)

A poorly made tap or die would/could be responsible for this. Can you beg, borrow or buy a different tap and die set to try them (or a tap or die by itself)?

Adjusting the die tighter might be a little help =or might not- but that would just be adding sloppiness to the thread to increase the number of diameters it will thread in, not a good idea if you are working toward precision and perfection.

And again, it might be something else entirely. I can't see it as being a complex problem though, since threading with a tap and die really isn't a very complex operation. A good tap and a good die combined with the correct drill size should produce acceptable results with little effort other than making sure the tenon and drilled hole are done properly and the threading is done parallel to their axix and not at an angle..

 

[frank123]

One additional thought. If you're using a M10 x 1 tap, any chance you could obtain a commercial M10 x 1 bolt and try threading it in to the barrel to see if it is still the same?

 

[Rich L]

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Unless you are using a bottoming tap you may not be tapping deep enough and getting a tapered female thread that gets tighter the farther in you go.

Yeah, I thought of that and have been running the tap in as far as the situation allows to get past the taper. That helps a little, but the problem persists. As I screw the pieces together, they screw pretty well at first, then after maybe 3 or 4 turns, they get tight, to the point that I cannot screw the male piece all the way in. That's when I start using my tap wrench and pushing to the side as I screw the tap in and out, gradually widening the joint so that the male piece willl screw all the way in.

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Sounds like you have a dull tap or possibly a bad one as Frank says (off pitch for some reason). If you're "screwing" around like that just trying to tap a simple hole something is wrong with the tap, I'd bet, or the material is too compliant. You're not trying to thread teflon, are you? Also, you say you're getting past the taper - are you sure? A taper tap can have anywhere from a 5 to 7 thread chamfer. If you're tapping soft stuff and it doesn't chip too easily try a plug or bottoming tap (bottoming for a finish pass).

You don't say what the material is but make sure your male and female threads are cleaned up after your threading. Did you measure your male thread major diameter and check that it's less than 10mm (just to make sure)? Can you measure your internal thread minor diameter to see if that makes sense? Make sure you don't have any fuzz or crap hanging off the crest of your threads otherwise that will bind up after some distance.

Are you using any lube at all? soap and water, cutting fluid, lard, cooking oil...?

Just some more thoughts...

Cheers,
Rich

 

[Robert111]

You may have either a tap or die that is not cut to the exact thread pitch.

For example a 1 mm die thread would thread into a .98 mm tapped hole for several diameters before the mismatch took up all excess clearance and started binding. (not necessarily the real numbers, just an example)

A poorly made tap or die would/could be responsible for this. Can you beg, borrow or buy a different tap and die set to try them (or a tap or die by itself)?

Well, I've been buying them at Victor, where a lot of others on this forum buy them.

Adjusting the die tighter might be a little help =or might not- but that would just be adding sloppiness to the thread to increase the number of diameters it will thread in, not a good idea if you are working toward precision and perfection.

And again, it might be something else entirely. Yeah, I'm suspicious it's a technique issue (see the note below in Rich's post) I can't see it as being a complex problem though, since threading with a tap and die really isn't a very complex operation. A good tap and a good die combined with the correct drill size should produce acceptable results with little effort other than making sure the tenon and drilled hole are done properly and the threading is done parallel to their axix and not at an angle..

Thanks for the ideas, Frank.

 

[Robert111]

Quote:
Sounds like you have a dull tap or possibly a bad one as Frank says (off pitch for some reason). If you're "screwing" around like that just trying to tap a simple hole something is wrong with the tap, I'd bet, or the material is too compliant. You're not trying to thread teflon, are you? Also, you say you're getting past the taper - are you sure? A taper tap can have anywhere from a 5 to 7 thread chamfer. If you're tapping soft stuff and it doesn't chip too easily try a plug or bottoming tap (bottoming for a finish pass).

You don't say what the material is but make sure your male and female threads are cleaned up after your threading. Did you measure your male thread major diameter and check that it's less than 10mm (just to make sure)? Can you measure your internal thread minor diameter to see if that makes sense? Make sure you don't have any fuzz or crap hanging off the crest of your threads otherwise that will bind up after some distance.

Are you using any lube at all? soap and water, cutting fluid, lard, cooking oil...?

Just some more thoughts...

Cheers,
Rich

I use vegetable oil spray. I didn't mention the kind of material, but it's all kinds--acrylic, ebonite, celluloid acetate (cebloplast), PR--all kinds. Because this happens with all my threading that goes more that 1/4" deep, I'm suspicious it's a technique issue. One thing you mention sounds an alarm: I don't clean out the hole after tapping. It's possible that the crumbs are getting forced in and compressing in the deeper threads. What's good for cleaning out the hole? Toothbrush is too big. Thanks for your thoughts Rich.

 

[mredburn]

compressed air or try a small shop vac. or paint gun brushes or gun cleaning brushes any small round bristle brush. When drilling out the hole for the tap i also give a little lee way making the hole very slightly larger if I can. on a m10 x.75 I will drill it more of 9.3 or 9.4 than 9.25. I find that some of the taps dont cut the threads as deep as others.

 

[Curly]

I clean the threads with a cotton swab (Q-Tips actually ). Any rough spots on the thread will pull fibres and let you know to run another pass.

 

[Jjartwood]

I'm just starting out with the threading of plastics (I've used taps and dies quite a bit
when I was building Hot Rods for a hobby ) so far I've found tight threads in plastic can be smoothed with a compound called rhodium glass polishing compound it is a powder form that is mixed with water and can be mixed quite thin I've placed it on the threads and worked it back and forth a few times and it "Laps " the threads to a uniform and smooth
feel,

 

[Russianwolf]

make your own bottoming tap.

Just need a material harder than what you want to cut. Aluminum or brass will work for resins and wood.

Use your die to thread a section of Aluminum. Once threaded take a dremel and cut some channels to allow for the shavings. Then chase the threads again and clean it up again.

So when you use you bought tap to make the threads, follow it up with your made tap. You should get full threads to full depth.

 

[Timebandit]

What size bit are you using? As Mike said, i would use a bit slightly larger than the perfect one for the tap. I always oversize on this. Also you may try chamfering the inside of the barrel threads and the cap/finial threads. I do this with my woodchuck and it lets the section and finial screw in nice and flush. You can also drill out the first few threads in the barrel or cap, but i find the slight chamfer to be much more pleasing to the eye, kind of a slight ramp, and i polish it up, so its nice and clean.

 

[Robert111]

compressed air or try a small shop vac. or paint gun brushes or gun cleaning brushes any small round bristle brush. When drilling out the hole for the tap i also give a little lee way making the hole very slightly larger if I can. on a m10 x.75 I will drill it more of 9.3 or 9.4 than 9.25. I find that some of the taps dont cut the threads as deep as others.

That much, eh? I have drilled a little large, but now I'll try even bigger. Thanks Mike.

 

[Robert111]

I clean the threads with a cotton swab (Q-Tips actually ). Any rough spots on the thread will pull fibres and let you know to run another pass.

Very good. And I've seen Q tips that have come out kind of ragged.

 

[Robert111]

I'm just starting out with the threading of plastics (I've used taps and dies quite a bit
when I was building Hot Rods for a hobby ) so far I've found tight threads in plastic can be smoothed with a compound called rhodium glass polishing compound it is a powder form that is mixed with water and can be mixed quite thin I've placed it on the threads and worked it back and forth a few times and it "Laps " the threads to a uniform and smooth
feel,

That's a great idea. I have some Semichrome that I know is abrasive, also the Hut's plastic polish.

 

[Robert111]

make your own bottoming tap.

Just need a material harder than what you want to cut. Aluminum or brass will work for resins and wood.

Use your die to thread a section of Aluminum. Once threaded take a dremel and cut some channels to allow for the shavings. Then chase the threads again and clean it up again.

So when you use you bought tap to make the threads, follow it up with your made tap. You should get full threads to full depth.

Sounds simple enough, Mike. Thanks.

 

[Robert111]

What size bit are you using? As Mike said, i would use a bit slightly larger than the perfect one for the tap. I always oversize on this. Also you may try chamfering the inside of the barrel threads and the cap/finial threads. I do this with my woodchuck and it lets the section and finial screw in nice and flush. You can also drill out the first few threads in the barrel or cap, but i find the slight chamfer to be much more pleasing to the eye, kind of a slight ramp, and i polish it up, so its nice and clean.

Yeah, I just started doing that Justin. I noticed Soligen doing that with the back corner of his Woodchuck in a video he made. Thanks!