Toolpost bolt hole threads?

DFWKen

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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
 
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.
 
Just messure the distance from the peak of one thread to the next peak.
 
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.
 
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.
 
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:
1stSuccesfullmm.JPG


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


Compound with the new bolt installed:
metrictoolpostboltinstalled2.JPG


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.:
DorianToolpostInstalled.JPG
 
We all have learned a lot from mistakes. Nice job there.:congrats:
 
I agree that the factory 4-way tool post is just dumb. It is at most a 2 1/2 tool post.
Pierre
 
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 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.
 
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