Advice on lathe Threading tools

[Tony Pratt 1Participant @tonypratt1]

Jim,

From memory Glanze only do 60 degree inserts but as you say it is the insert not the toolholder which determines the thread form, APT phone # is on their website 0141 892 1010, only one holder is required for both 55 & 60 degree threads.

Tony

[SillyOldDufferModerator @sillyoldduffer]

I'm confused too, but I think Jim may be right. I found 55° inserts to fit ISO holders readily enough, but not to fit the ISO size holders that happen to be sold by Glanze. I didn't look very hard! RDG do sets that take 55° and 60° inserts, and I expect others do as well. (Mine does, but I can't remember where it came from!)

Dave

[John BaronParticipant @johnbaron31275]

Posted by Jim Beagley on 20/05/2020 12:17:14:

Posted by John Baron on 20/05/2020 11:18:26:

Posted by Jim Beagley on 20/05/2020 10:35:02:

I’ve been looking for a suitable Glanze internal threading indexable holder and apparently they only do ones for 60” inserts.
I don’t really want to pay £60 for a Kolroy one although it will do both 60” and 55”.
Can anyone recommend an alternative?

I looked at APT but there’s not number to call them that I can find.

cheers
Jim

Hi Jim, I would check that information very carefully, I don't know any carbide insert that will do both angles ! It will be one or the other not both. I doubt that it would be double ended in order to do that.

FWIW. I pay around £8 for ten 60 degree ones and around £14 for 10 off 55 degree ones. However getting stuff out of China is difficult at the moment.

Edited By John Baron on 20/05/2020 11:20:48

Edited By John Baron on 20/05/2020 11:21:44

Hi John. I was looking for a holder that would take both 55 and 60 degree inserts. Sorry if I was unclear.
I spoke to Chronos and they say the Glanze ones will only take 60 degree but I’m confused by that as I suspect it’s just the insert that sets the form angle. Am I wrong? I much prefer the cost of the Glanze holder (£30) to the Kolroy one (£60).
Jim

Ah, you didn't mention the holders / boring bars ! The bars that I have will accept either of the 60 or 55 degree carbide inserts. The one that nobody seems to do is the 47.5 degree ones for BA threads. Luckily for me a friend has ground a couple of HSS cutters for those. 2 mm square HSS that fit into a hole drilled into the end of a short length of 12 mm square bar, with a 4 BA hex socket grub screw.

[Jim BeagleyParticipant @jimbeagley46363]

OK so I've gone for internal and external ER16 holders from APT, and a selection of metric external inserts to practice with, plus the 8TPI BSW internal for my back plate project.

Wish me luck!

[old martParticipant @oldmart]

Start practicing on an external thread. Get a length of 1" bar aluminium and, say, if it is 6" long, then turn down half to 3/4". Turn it round and chuck up the smaller end. You should have a larger diameter outboard with a gap between it and the chuck of an inch. This gives you a runoff area to disengage the leadscrew well before crashing. Run the lathe at its lowest speed. Before engaging the leadscrew, bring the tip of the insert up to the work so it just leaves a witness and zero the cross slide scale. Move the saddle out of the way of the work, and engage the feed nuts when one of the numbers on the threading dial comes round. For a beginner, it is safer to wait for the same number to come round every time you take a cut. Take the first cut at the zero position and the tool should leave a tiny helical groove. Check the pitch of this groove to ensure it is the same as the pitch you have set. The cross slide must be backed off past zero every time you bring the saddle back to the right. Keep the compound parallel to the axis of the bed, any adjustments there are for when you get more practice. The first cut can be up to 1/5 of the thread depth, but as you get deeper, there is progressively more metal cut, so the depth of cut should be less at each pass, ending up at 0.001" and then spring cuts.

[Jim BeagleyParticipant @jimbeagley46363]

I have been looking at the lathe this morning with a view to starting threading operations over the weekend, and I was checking out the gears.

On the cover plate (which I dont have) is a picture showing a changeable stud gear, a 100T to 127T converter gear, and a 56T screw gear,
The table I have then shows the different options for metric cutting.

I don't have the 100/127 gear, but an 85T and the stud gear I have is 20T which doesnt appear in the metric table anyway.

So to the questions:

Is the 85T the 'standard' fitment to give the TPI on the gearbox?

Are the gears the same as the myford ones? The ID seems the same at 5/8.

Cheers all, and thanks for the continued help.
Jim

[Martin ConnellyParticipant @martinconnelly55370]

The Smart and Brown Model M gears are 16DP, can't remember the pressure angle, I'm pretty sure the Myford ones are different and not interchangeable with them.

The gear combination you describe with 100,127 is for cutting metric threads on an imperial leadscrew machine or for cutting imperial threads on a metric leadscrew machine. You say you don't have a cover plate so I am not sure if you have an imperial or metric leadscrew.

The first thing to check is the leadscrew pitch. The one on mine is 6 TPI imperial. I suspect a metric one will be similar with 4mm pitch.

If you have the imperial leadscrew it is just a matter of putting together a gear train that will give the required tpi without the 127 tooth wheel.

If you have a metric leadscrew you need a 127 tooth gear wheel for accuracy but close may be possible if you have a good selection of gears.

So let us know what the leadscrew thread is and what you have in the way of change gears.

Martin C

[Martin ConnellyParticipant @martinconnelly55370]

I have found an image on the internet that looks like what you are describing for doing metric threads on an imperial leadscrew. It looks to me like you need a 24 tooth stud gear driving either the 100 tooth wheel or the 127 tooth wheel as an idler and then the 56 tooth screw cutting gear. By idler I mean one that does nothing to change the thread pitch, it is both driven and driver in the system. So the spur gear drives the idler and the idler drives the screw cutting gear.

I am making this suggestion based on the fact that the image shows the 127 tooth being driven by a 48 tooth wheel and the 100 tooth wheel driving a 56 tooth wheel with the gearbox at 8 to give a 6mm pitch. Changing the 48 tooth to 24 should halve the pitch to 3mm. Not using the 127/100 combination except as an idler will increase the pitch slightly to 3.81mm so the gearbox will have to be set to something other than 8, possibly 7 or 6 as you want 3.175mm pitch which is 8 tpi.

Martin C

[Jim BeagleyParticipant @jimbeagley46363]

Hi Martin.
The lead screw is 8TPI and the whole lathe appears to be imperial.
The gearbox refers to either a 20 or 40 tooth stud gear for different TPIs but I only have the 20 tooth gear.

I have just cut a really rough thread at the setting shown for 8TPI, and amazingly, it’s correct. My first thread

I have that diagram similar to the one you mention with a 100/127 idler. The diagram I have then refers to different stud gears and gearbox setting for different metric TPIs

what I don’t get here is that the gearbox has 2 gear settings, and I don’t actually have any of the listed stud gears

[Martin ConnellyParticipant @martinconnelly55370]

Looking at that chart it looks like the gearbox has settings for imperial settings from 8 to 160 tpi. The standard set up presumably has the 56 tooth wheel as the screw gear and a 20 tooth stud gear and the 127/100 gear set as an idler. You can work this out from the chart you have showing a 40 tooth stud gear for a 5mm pitch thread and the gearbox set to 8.

If you have a 20 tooth stud gear instead you get 2.5mm pitch. If you multiply this by 127 and divide by 100 you get 3.175mm pitch. 8 x 3.175mm is 25.4mm. So with the gearbox set to 8 with the 20 tooth stud gear you will get 8 tpi.

Martin C

[Jim BeagleyParticipant @jimbeagley46363]

That maths has made my head hurt. I’ll have to make a spreadsheet

[Martin ConnellyParticipant @martinconnelly55370]

Does your lathe have a gearbox with a plate like this?

Martin C

[Jim BeagleyParticipant @jimbeagley46363]

Posted by Martin Connelly on 21/05/2020 23:24:54:

Does your lathe have a gearbox with a plate like this?

Martin C

Yes, exactly the same.

[Martin ConnellyParticipant @martinconnelly55370]

Somewhere there should be a diagram similar to this, either on the lathe or in the manual you probably don't have.

This not too clear diagram is a side view of the change gears. A is your stud gear, B is your 127 tooth gear, C is your 100 tooth gear and D is your 56 tooth screw gear. The left hand illustration shows the setup for metric thread pitches, the right hand illustration shows the setup for imperial threads per inch settings. In the right hand setup the B gear is an idler and so the tooth count is not too important, I suspect that if you have the 20 tooth stud gear in then the 127 tooth gear will work as an idler. If you had a 40 tooth stud gear then you may find you need to use the 100 tooth gear as an idler.

Anyway, from the gearbox plate we see that to do an 8tpi thread we need the stud gear (label A above) to be 20 teeth. We need the left hand gear selector to be in position A and the right hand gear selector to be in the leftmost position.

From the gearbox label we can see if we just change the left hand gear selector progressively through positions A, B, C, D and E we double the tpi count with each move. This means we are halving the lead screw revolution (relative to the spindle) with each move towards the right. This is quite typical for a lot of lathe gearboxes with two gear selectors. One selector has this halving/doubling action. The right hand lever has gears with a tooth count in ratios of 16, 18, 20, 22, 23, 24, 26, 28. We can tell this because just changing the right hand lever produces threads with these counts going from left to right on the third row. The actual number of teeth may be double this. This combination of change gears and 2 ratio selectors gives all the threads you are likely to need but is not comprehensive, BA threads for example are not included.

I don't know if you have a thread dial indicator but luckily for you an 8 tpi thread and an 8 tpi leadscrew means you can engage the half nuts anywhere on the leadscrew and be in the correct position for multiple passes to cut the thread.

Martin C

[Jim BeagleyParticipant @jimbeagley46363]

Hi Martin and thanks for your time in such clear explanations.
luckily I do have the thread dial indicator and I used it to cut my first (ratty) thread last night.

I do get that the 127/100 gear converts the imperial system to metric threads – I guess I will have to try and source one of these. At the moment there is a simple single 80T idler gear between the 20T stud and the 56T drive gear.
I also now more fully understand the gearbox functionality – thanks.

I guess the 40T stud has also got lost before I had the machine.
Will the Myford gears I see advertised fit? The ID seems the same but I am unfamiliar with PD and PCD.

Best, Jim

ps here is my horrible thread, but it was the wrong insert and the wrong feed but it’s a start

[Martin ConnellyParticipant @martinconnelly55370]

HPC Gears has a useful technical library. It will help you to find out what the designation of your gears is, I think it will be 16DP for the change gears as that is what the other Smart and Brown lathes use. Not being certain the tables from HPC will allow you to check if this size matches what you have. I think Myford gears are smaller but I am sure the information on them is available either from some kind Myford owner on this forum or just a general google search.

HPC gears technical references

Martin C

A quick search turned up a thread on this forum called Myford change-gear pressure angle and in there it says Myford gears are 20DP. This means they will not mesh with 16DP gears.

Edited By Martin Connelly on 22/05/2020 10:33:28

[Martin ConnellyParticipant @martinconnelly55370]

Just a comment regarding thread cutting, this process really does benefit from a quality thread cutting oil. I use a small paintbrush and Rocol RTD oil but others are available.

The other thing I have done is an aluminium dummy spindle nose (not bored) to check the threading progress in backplates as is cut. Before you start on an actual backplate this would make a good project to practice threading on. I'll dig out either the dummy or an existing photo.

Martin C

Edited By Martin Connelly on 22/05/2020 11:47:35

[Jim BeagleyParticipant @jimbeagley46363]

Hi Martin.
Great minds actually. It was also my intention to make a dummy spindle nose to check the threads, plus it’s going to be simpler for me to start with the external I think. I’ve got some MS steel blanks of the right size in order too.
move got some Moly cutting grease. Maybe that’ll work.

[old martParticipant @oldmart]

By all means use lubricant on steel when you cut threads, I always use a little CT90 spray. When you cut cast iron, do it dry, and a vacuum cleaner and magnets help to reduce the mess of CI powder, and take care to remove all the dust from the lathe afterwards. I made a dummy spindle nose for the Model A, the difficulty is getting it exactly the same size. As I mentioned before, when your insert just makes a mark on the 1.750"/1.751" register, the thread size is exactly right. These large 8 tpi threads have a lot of leeway in the size, going a bit loose is much preferable to tight.

You haven't mentioned how you intend to hold the plate as you machine it.

[Jim BeagleyParticipant @jimbeagley46363]

Hi old Mart.

I have a 3 jaw with reversible jaws that I hope will be big enough to hold the boss.
That makes me thing though – which side should I be cutting the thread from. Using your method I would need to be seeing the inside of the boss register, so that wont work too well.

Perhaps the outside of a 5" plate will fit into the reversed jaws of my 6" 4 jaw?

In the end, I guess I could reverse it and bolt it to the 3 or 4 jaw plate with some temp holes?

[old martParticipant @oldmart]

As you don't have a faceplate, holding a blank will be difficult. Therefore, I would tend to go for a part machined, one with a 1 1/2" Boxford thread. It will be easier for you to hold and there is enough meat in the bore to go to 1 3/4" S&B. Being machined will enable you to attach it to one of your chuck backing plates by drilling and tapping it. A four jaw independent chuck can be used as a faceplate if tee nuts are made to fit in the jaw slots. You could also drill and tap the four jaw between the jaws, I have done this mod on both the chucks at the museum to attach balance weights. Chronos have a 6" one that would suit.

**LINK**

[Martin ConnellyParticipant @martinconnelly55370]

It's a while since I did mine but I think I held mine in my 4 jaw. I can turn an 8" diameter so a plate at 6" or a little more could be held with clearance between the lathe and the jaw protrusions. I can't remember taking any photos of the job but I know that I unscrewed the chuck and backplate to check against the spindle then remounted it to take a bit more off without taking the backplate out of the chuck. I think towards the end I was hand chasing it, polishing it with a small stiff wire brush and scotchbrite to get a smooth fit on the thread rather than use the threading cutter driven by the lathe. It took time but did the job.

Martin C

[Martin ConnellyParticipant @martinconnelly55370]

I have just worked out that I have done this job 4 times now. The first was to make a faceplate that could also be used as a catch plate for turning between centres. This was bought as one for another machine that was then modified to suit much as old mart is suggesting with the Boxford backplate. I ended up with a ragged thread which is why I ended up with the hand chasing and polishing on the rest. The next one was for a 100mm chuck then one for a spare 6" chuck and finally for an ER32 chuck, pictured below. You can see the thread witness mark on the register that old mart mentioned somewhere.

Martin C

[old martParticipant @oldmart]

That Chronos 6" plate was the only one that I could see that had a decent diameter boss for increasing the thread diameter, and the price increase over an unmachined blank is well worth the reduction of CI mess. The 160mm od could be reduced to 5" if that was the size required using the boss to chuck up on normally, and then the four jaw could hold it easily boss to the right. The advantage of using the four jaw is that the plate will then stand off the chuck face, giving a little runout when threading. Boring the register and the thread bore and threading should be done together to ensure perfect concentricity. To check the thread, which will be fine, the cheat is to unscrew the chuck, and try out the thread on the spindle without taking the plate out of the chuck. Screw it back on only if the backplate needs another pass or two of threading.

Edited By old mart on 22/05/2020 17:03:49

[Jim BeagleyParticipant @jimbeagley46363]

To check the thread, which will be fine, the cheat is to unscrew the chuck, and try out the thread on the spindle without taking the plate out of the chuck. Screw it back on only if the backplate needs another pass or two of threading.

Ha – cunning!

I very much appreciate all these tips and advice. I know you guys must have answered these questions before, so its doubly appreciated. I have just ordered the 6" semi machined boxford plate from Chronos.

Any clever solutions for knocking up a manual winding handle?

[Author]

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