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Toolpost bolt hole threads?

DFWKen

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#1
G0740 Lathe:
Does anyone know the metric (I assume its metric because it isn't SAE) Threads per mm for the big hold-down bolt in the middle of the 4-way toolpost. (or the T-nut threaded hole might be a better description).

Instead of trying to get a new T-nut made for my Dorian Quick Change toolpost, I want to simply turn a new bolt. Should be easy enough to do; but my Metric thread gauge doesn't go that course.

I'm thinking that it's a common thread size that fits any of the 13" and larger lathes.

I really like the massive 4-way tool holder except for the need to have a bunch of shims on hand and having to shim with every tool change. The Dorian BXA looks dinky in comparison. A CXA would look better.;)

Ken
 

fitterman1

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#2
If its 14mm dia then its either 2mm, 1.5mm or even 1.25mm pitch. (1.25 is sparkplug - unlikely)
If 16mm its either 2mm or 1.5mm pitch. A metric steel rule will tell you what it is.
Make sure your toolpost (bxa,cxa) will allow your tools in their holders to sit on center.
 

kd4gij

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#3
Just messure the distance from the peak of one thread to the next peak.
 

DFWKen

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#4
Just messure the distance from the peak of one thread to the next peak.
That's hard to do to within 1mm. If they measured it per cm or inch, would be so much easier.
And I just thought about this. I can multiply by 10 to get cm and then how many threads in one cm for better resolution. I'll try that and see if it comes up to a standard pitch. TPI is so much easier because it is a whole number of threads in one inch.
 

DFWKen

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#5
If its 14mm dia then its either 2mm, 1.5mm or even 1.25mm pitch. (1.25 is sparkplug - unlikely)
If 16mm its either 2mm or 1.5mm pitch. A metric steel rule will tell you what it is.
Make sure your toolpost (bxa,cxa) will allow your tools in their holders to sit on center.
Thanks. I'm going to check to see if it's 2mm, 1.5mm or 1.25mm. I'm assuming that the number is one thread (peak to peak) in a mm. (i.e. 2mm for one thread)

And I just googled metric and see that it's measured in "pitch" instead of tpi. No wonder the lathes thread chart seemed backwards. New wrinkle in my brain today.

The Dorian BXA is supposed to cover 13 - 15" swing. My 14" is right in the middle so it should be good. And I actually checked it yesterday to see if I could get the cutting point on the center of the workpiece and I can with room to adjust up or down. But it really looks dinky on the big (to me) lathe.
 

DFWKen

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#6
Thanks for the help and advice, KD4 and Fitterman. They got me going in the right direction.
I finally figured out the thread pitch (and that it's not measured in TPI). It is 2mm. There are five different levers to set on this lathe to get the carriage running in the right speed for the threading in relation to the spindle. Everything much be right or a fail will result. And I had several fails before success; each fail resulting in something new learned.
When my scratch passes matched the desired pitch, I began threading. That's when I learned something else new.
My lathe will do SAE threads all day long using the threading dial. But no such dial for Metric. I finally figured out what the placard means, "For Metric, the Half-Nut nut must stay engaged." HUH? But now I get it. The feed screw is SAE; so the threading dial will only indicate SAE threading. (I think that's right)

No problem, I'll just reverse the feed and back up. Then, set the compound in a few thousandths and go back forward again for each successive cut. Big Fail, times three before I figured out what was chipping my threading tool insert. 3 inserts in the trash and I'm wiser now. Never back up. Never even stop! (insert #4 broken). Back out of the threads quickly at the end with the half-nut still engaged, pull the big carriage lever back to center to stop the lathe and step on the brake as it winds down to avoid hitting the chuck. I love having a brake! I must prepare for the stopping procedure with hands and feet on the controls and rehearse the sequence in my mind for each pass.

All those failures and muddling through my self-taught learning curve and I have 1 end of the new toolpost hold-down bolt threaded metric 2mm pitch. It only took about 6 hours.

Did much better on the other end of the bolt. Decided to stick with metric and use the lever that came with the 4-way (which has metric threads as well) instead of a simple ugly hex nut that requires a wrench each time. This threading operation only took me about 10 minutes and no broken tooling. Happy!:)

Removed the 4-way tool holder and installed the Dorian using my new metric-threaded on both ends bolt. and it works great. The hold-down bolt was made from a bar of stainless that I had in the scrap pile.
First thing I did when the Dorian QCTP was installed was to part a rough end off the bar. It was so nice to be able to easily center the parting tool's cutting edge on the workpiece. WHY IN THE WORLD DO THE SELL LATHES WITH THOSE 4-WAY TOOLPOSTS? DOES ANYONE LIKE THEM?

Here are a few pictures:


First successful metric threading, fresh out of the chuck:


After threading both ends (bottom for the T-nut and top for the holding bolt lever:


Compound with the new bolt installed:


Dorian Quick Change Toolpost installed (with the 4-way sitting aside for comparison). I bought the Dorian QCTP used on eBay for $249 shipped. Very happy to finally see it on a lathe It looks dinky, but the up/down adjustment is right in the middle of its 13" to 15" lathe swing spec.:
 

kd4gij

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#7
We all have learned a lot from mistakes. Nice job there.:congrats:
 

pdentrem

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#8
I agree that the factory 4-way tool post is just dumb. It is at most a 2 1/2 tool post.
Pierre
 

kd4gij

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#9
I disagree. At work we have a 14x40 lathe with a 4 way tool post. 1 turning and facing 1 45 degree for chamfering 1 for undercutting and one for threading. It is much faster than a QCTP
 

DFWKen

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#10
I disagree. At work we have a 14x40 lathe with a 4 way tool post. 1 turning and facing 1 45 degree for chamfering 1 for undercutting and one for threading. It is much faster than a QCTP
I can see how they'd be an advantage once set up with tooling and adjusted with shims. My tooling is not of constant height and getting it shimmed was a pain.

I liked the quarter-turn stop that allowed the 4-way to rotate in precisely 90-degree steps. But the QCTP will be much more efficient and less frustrating for me. I've already centered several holders with tooling; ready to slap onto the Dorian, tighten, and make chips.
 

fitterman1

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#11
"WHY IN THE WORLD DO THEY SELL LATHES WITH THOSE 4-WAY TOOLPOSTS?"
Because they are basic and cost less. One of the lathes at work has a 4 way thats 10" square, a 2" boring bar resides in it permanently.

Can you imagine the size of the QCTP for that size? Let alone the cost.
I noticed you didn't chamfer the end of your bolt prior to threading in the top photo. May I suggest you do that in future because it looks nicer and it is a transition point for the insert whereby it doesn't get hammered by being forced into a 90 degree edge. Overall a job well done and in stainless too.
 
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kram390

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#12
Oxtool has made a video about this subject, called:
Metric Threading with an Inch Lead Screw

I cant add links yet, because i'm new here.
I mostly do metric threading, with an imperial leadscrew. But I dont have an threading dial yet, so cant use this trick unfortunately.
 

DFWKen

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#13
"WHY IN THE WORLD DO THEY SELL LATHES WITH THOSE 4-WAY TOOLPOSTS?"
Because they are basic and cost less. One of the lathes at work has a 4 way thats 8" square, a 2" boring bar resides in it permanently.

Can you imagine the size of the QCTP for that size? Let alone the cost.
I noticed you didn't chamfer the end of your bolt prior to threading in the top photo. May I suggest you do that in future because it looks nicer and it is a transition point for the insert whereby it doesn't get hammered by being forced into a 90 degree edge. Overall a job well done and in stainless too.
You're right . . . I didn't chamfer first. I usually do; but had so many failed attempts that I forgot. If it had any problems starting into the threaded hole, I was going to chamfer afterwards. But the threads started easily every time.
I was wondering what flaws in my work would be noticed; and welcome all advice and constructive criticisms.

Ken
 

fitterman1

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#14
Ken, Considering your work was with stainless, it looks fairly good for a first attempt. Looking at your second photo which is the clearest I can see faint chatter marks. Not a serious issue unless its a production run.
Feeding in square on will produce this amongst other factors. Feeding in at 29.5 deg may have eliminated it. Its a good job, nothing to worry about, don't forget practice makes perfect.
 

DFWKen

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#15
Ken, Considering your work was with stainless, it looks fairly good for a first attempt. Looking at your second photo which is the clearest I can see faint chatter marks. Not a serious issue unless its a production run.
Feeding in square on will produce this amongst other factors. Feeding in at 29.5 deg may have eliminated it. Its a good job, nothing to worry about, don't forget practice makes perfect.
Thank you.
I actually did feed with the compound set at about 29 degrees so the tool only cuts into one side of the thread. I can see the result of the chatter, too. I had the workpiece as close to the chuck as I dared, but didn't use a center to hold the free end. That might have helped.
Yeah, I could use some more practice; and I'll get it as I work with the new lathe. I've had a 12x36 for almost 15 years. This new lathe is a bunch more substantial and a heck of a lot of fun to use.
 

fitterman1

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#16
Thank you.
I actually did feed with the compound set at about 29 degrees so the tool only cuts into one side of the thread. I can see the result of the chatter, too. I had the workpiece as close to the chuck as I dared, but didn't use a center to hold the free end. That might have helped.
Yeah, I could use some more practice; and I'll get it as I work with the new lathe. I've had a 12x36 for almost 15 years. This new lathe is a bunch more substantial and a heck of a lot of fun to use.
Stainless is a pain to work with sometimes, its soft but tough at the same time. On smaller diameter stuff I always try to use a center (live or dead) to prevent chatter.
Keep up the good work.
 

tmarks11

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#17
That's when I learned something else new.
My lathe will do SAE threads all day long using the threading dial. But no such dial for Metric. ... I'll just reverse the feed and back up.


Not just your lathe. Every lathe. Either the leadscrew is spaced for inches or for metric. You don't get both, unless you put a god-awful amount of gearing in the apron to convert one to the other.
 

whitmore

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#18
My lathe will do SAE threads all day long using the threading dial. But no such dial for Metric. I finally figured out what the placard means, "For Metric, the Half-Nut nut must stay engaged." HUH? But now I get it. The feed screw is SAE; so the threading dial will only indicate SAE threading. (I think that's right)
The big difference in metric pitch and unified national (inch) "tpi" is that
there's almost always an integer number of identical threads per inch. So a threading dial can
tell you for sure that the engagement is at exactly +/- N inch from the start,
then the half-nut will engage and travel to the partly-cut thread.
For even threads (6 tpi or 32 tpi but not 27 tpi) it will also do this at
exactly 1/2 inch, so you can use another number (evens or odds only) on
the thread dial... the threading screw is 8 per inch, typically.

If your need is for 10.5 threads per inch, your thread dial isn't much help.

But, standardized metric pitches (M4 x 0.7mm, M12 x 1.75mm, etc.) don't
exactly divide (with no remainder) into 1.0 cm, so the whole system is incompatible
with the threading dial trick.

It would take a dial with a quickchange gear cluster, and a table of which to use...
Actually, now that I think of it, a digital readout could be arranged, it'd be
easier than a gearbox. Still wouldn't work with an inch threadscrew, though.
 
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USMCDOC

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#19
You all talking about MM's made me drag this out!

MMPitchGauge.jpg
But if i had a lathe right now.. i would like to have to have the QCTP myself..
 
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