Thread: Threading Advice…..Again!

I have read this thread with interest. Two questions came up. I understand the use of thread wires and gauges, but aren't thread micrometers possible too?
And if you swivel the compound, wouldn't a indicator give you the actual infeed too?
Thanks,

Peter

Thread mics would be best in critical situations,although a little expensive,the same as GO/NOGO gauges
If you swivel the compound you then need to check depth off a chart or do the calcs associated with it..

Originally Posted by pipeclay

Thread mics would be best in critical situations,although a little expensive,

Generally more than a little expensive, particularly if you want top name brads like Mitutoyo etc. Bearing in mind that while a 0 to 1"mic or 0 to 25MM metric equivalent, with interchangeable anvils will measure quite a few different threads, the sizes up (1-2" say) cover a much smaller range. Also the micrometers often come with only one or two anvil sets, and a few anvil sets can cost more than the micrometer, so it can get expensive pretty quickly. Easy to blow a grand or so if you have it to spare.
Having said all that, there are some interesting offerings on yank ebay right now, and some with lower than usual pricing I would have thought. If you search with the term thread micrometer, a set of PD thread wires, +1-2"Mity mike and a set of angle gauges comes up, all for about AU$65 BIN +$26 or thereabouts postage. Very tempting, I'm not sure how I'm resisting
Rob.

Originally Posted by simonl

Mind you, if you make your major diameter within the specified tolerance and you feed in at the correct depth, how can you get it wrong anyway? It's just a recipe.

Simon

Easy to get it wrong if your tool profile is wrong or your lathe is a bit worn and telling fibs on how deep you have cut..

Thread micrometers are probably OK, but I have not seen a set yet that have all the anvils required, plus the micrometers only do 25mm steps..

Quite a few tips and tricks on the usual forums on how to use thread wires and hold them.... Tasmanians find it easier as they can use their tail to hold the third wire

Originally Posted by .RC.

.. Tasmanians find it easier as they can use their tail to hold the third wire

+, with 2 heads we're twice as smart!

One method I use when I have full profile inserts is to cut the thread until the od is a bit under the nominal size. Works great 99% of the time. The other 1% I blame the bloke who made the nut .

Originally Posted by cba_melbourne

That is why I find it best NOT to set the compound to 29.5 degrees. If one leaves the compound parallel to the bedways, one sets the depth of cut exactly as per the cross slide dial - no math needed, no chance for errors, no thread wire needed..... Of course, on a lighter lathe one has to advance the compound sideways a bit for every pass, to ensure tool cuts on the shoulder. Then final cut is a plunge cut. And as you say, turning the major diameter to tolerance is dead easy. Advancing the cross slide to no more than the specified thread depth is very easy too, proper thread depth is almost guaranteed (provided the basics are right such as tool is sharp and at center height and lubricated and machine is not totally worn out and one does not pick up the phone halfway through the job....)

Definitely no need for thread wires, unless you are really after a precision thread (for something other than just a fastener thread). And even then, this 3 wire technique is cumbersome to use at best. A go-nogo thread hauge is far easier to use for repetition work.

I've never tried plunge cutting a thread. I have just assumed the results would be disappointing since my lathe is no monster. I don't set my compound to 29.5 degrees, I did when I first started learning and wondered why my thread profiles looked like a saw tooth. Then I realised that my particular lathe manufacturer saw fit to make 0 degrees when the compound is parallel to the bed ways! So it's 60.5 degrees for me, well actually I have no idea what I set it to with any real accuracy but it's a smige more than 60, which equates to a little less than the required 30 degrees ( for a 60 degree V thread)

From the required thread depth (minus 0.05mm) I work out the compound depth required from the hypotenuse of that triangle and multiply in that correction factor, feed in that amount. Then I plunge the last 0.05mm with the cross slide to achieve the full form from the tool.

It's a system that seems to work well for me but I have always had the corresponding threaded part to test fit and adjust the depth if needed. This will not always be the case and so thread wires seem to be a good investment.

Simon

Originally Posted by simonl

I've never tried plunge cutting a thread. I have just assumed the results would be disappointing since my lathe is no monster. I don't set my compound to 29.5 degrees, I did when I first started learning and wondered why my thread profiles looked like a saw tooth. Then I realised that my particular lathe manufacturer saw fit to make 0 degrees when the compound is parallel to the bed ways! So it's 60.5 degrees for me, well actually I have no idea what I set it to with any real accuracy but it's a smige more than 60, which equates to a little less than the required 30 degrees ( for a 60 degree V thread)

From the required thread depth (minus 0.05mm) I work out the compound depth required from the hypotenuse of that triangle and multiply in that correction factor, feed in that amount. Then I plunge the last 0.05mm with the cross slide to achieve the full form from the tool.

It's a system that seems to work well for me but I have always had the corresponding threaded part to test fit and adjust the depth if needed. This will not always be the case and so thread wires seem to be a good investment.

Simon

Simon, I am not sure if you did understand the technique for threading with the compound set parallel to the ways. This is not a single plunge cut. The thread is cut in several passes. And you actually cut on one edge of the cutting tool, just like with the other 29.5 degree technique. It is just the way how you achieve this that is different. You cut one pass with the left cutting edge, next with the right, and so forth. Only the very last cut is a very light plunge cut to get the profile right. Works well on light hobbylathes.

Maybe it gets clearer if I list in sequence for your M22x1.5g6 thread

- OD is finished to tolerance, like 20.4 to 20.6mm for g6
- advance threading tool until tip just touches the OD (use cigarette paper if needed)
- zero cross slide dial (of course without slackening the backlash)
- zero compound slide
- go to thread start and engage threading gear
- advance cross slide for first pass say 0.25mm and cut first pass
- slacken cross slide and return to thread start
- offset the compound slide by 0.1mm to the left (that is 0.1mm past the backlash to the left)
- advance cross slide to 0.5mm and cut second pass
- offset the compound slide by 0.1mm to the right (that is 0.2mm past the backlash to the right)

and so forth, until you come to the last pass, where you put the compound to 0 (always accounting for the backlash of your slide) and do a last plunge cut (plunge cut = cutting equally on both sides of the tool).

The amount of passes that you do depend on the pitch, as well as how rigid the lathe, material etc.
I choose by feel and experience as I go. But there are tables that one can use as a guide for the first time. This is what such a thread cutting table says for M1.5

pass 1 in-feed advance 0.26mm
pass 2 advance 0.23mm
pass 3 0.17mm
pass 4 0.14mm
pass 5 0.12mm
pass 6 0.06mm (final plunge cut)

For other pitches, these are recommended figures for number of passes and progressive in-feed for each pass

M1.25 - 6 passes 0.22, 0.19, 0.14, 0.12, 0.10, 0.06
M1.5 - 6 passes 0.21, 0.17, 0.13, 0.11, 0.06
M1 - 5 passes 0.21, 0.17, 0.13, 0.11, 0.06
M0.75 - 4 passes 0.19, 0.15, 0.11, 0.05
M0.5 - 4 passes 0.12, 0.1, 0.07, 0.05

Of course one can calculate the exact amount of compound side offset required for each pass, but it really is not that critical and after a short time you do that just by feel and experience.

Sorrt mate. I know what you mean now. I have heard of that technique. Its interesting how everyone gas their own technique they like and get godd results with. Ive used my method which I picked up from reading the workshop series on threading (they list 3 methods from memory) and ive got to a stage where its now routine, even if I havent threaded for 12 months.

Cheers.

Simon

Originally Posted by Ropetangler

+, with 2 heads we're twice as smart!

Well, perhaps...

How do you arrive at the IQ of a crowd?

Take the average IQ of a single person then divide by the number of people in the crowd.

Apply this logic to double-headed Tasmanians and what is the result?

Risdon Vale.

PDW

Originally Posted by PDW

Well, perhaps...

How do you arrive at the IQ of a crowd?

Take the average IQ of a single person then divide by the number of people in the crowd.

PDW

That maths does not seem right…..

Simon

Originally Posted by simonl

That maths does not seem right…..

Simon

I'm only an immigrant Tasmanian, I don't have to be able to count to 2....

PDW

Originally Posted by PDW

I'm only an immigrant Tasmanian, I don't have to be able to count to 2....

PDW

Computer programmers can only count 0 and 1 can they not... I cannot program computers so never got past 0... In any case this is Qld here, still the 1950's so no computers..

Originally Posted by .RC.

Computer programmers can only count 0 and 1 can they not...

Depends on what number base you work in...... a lot of Tasmanians can work in base 12 by counting on their fingers.....

PDW