Tom Lipton metric threading demo & article link he refers to
http://conradhoffman.com/metricthreading.htm
http://conradhoffman.com/metricthreading.htm
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CX701 gearbox questions
- Thread starter PaulL
- Start date
And success! I have made a part!
Thanks particularly to Susquash who spent a while with me going over screw threads and the screw dial. I was close, but he closed the gap.
I'm not at all pleased with my surface finish - it's off the first tool that I've ground myself, and it's, um, sub-par. Works for this piece which is hidden from view.
I did learn a new way to screw up metric threads on my lathe however. The instructions are clear: leave the half-nut engaged, stop the motor at the end of the cut, back out your tool, put the motor in reverse, and engage the motor to get back to the start.
Note that it says "put the motor in reverse". It does not say "put the feed screw in reverse". But what could be the harm? The feed screw lever feels better in-hand than the awful motor direction switch (which I'm going to have to replace with something nice). So what happens? As you move it you sometimes change which tooth in the gearbox gets engaged, shifting the carriage just a hair. But sometimes not! Most times not! Which led me to believe it was fine, until it missed and gouged my threads up.
Lesson learned: leave the *whole* transmission engaged when cutting metric threads. Or at least have a perfectly repeatable way to get the exact same teeth all along whenever you want to move your carriage.
Another fun bit - thanks to RobinHood for the link to chasing threads. I had to do it once - my first fit of the tool post thread was too tight. I had marked alignment of the part relative to the chuck, but of course I needed to reset the tool in the thread. Easy as pie - between the cross-slide and the compound I was able to adjust the tool to just kiss the right hand face of the thread. I was able then to advance my spindle by hand to make sure I was tracking right, and got off another couple of thou to a perfect fit.
Thanks particularly to Susquash who spent a while with me going over screw threads and the screw dial. I was close, but he closed the gap.
I'm not at all pleased with my surface finish - it's off the first tool that I've ground myself, and it's, um, sub-par. Works for this piece which is hidden from view.
I did learn a new way to screw up metric threads on my lathe however. The instructions are clear: leave the half-nut engaged, stop the motor at the end of the cut, back out your tool, put the motor in reverse, and engage the motor to get back to the start.
Note that it says "put the motor in reverse". It does not say "put the feed screw in reverse". But what could be the harm? The feed screw lever feels better in-hand than the awful motor direction switch (which I'm going to have to replace with something nice). So what happens? As you move it you sometimes change which tooth in the gearbox gets engaged, shifting the carriage just a hair. But sometimes not! Most times not! Which led me to believe it was fine, until it missed and gouged my threads up.
Lesson learned: leave the *whole* transmission engaged when cutting metric threads. Or at least have a perfectly repeatable way to get the exact same teeth all along whenever you want to move your carriage.
Another fun bit - thanks to RobinHood for the link to chasing threads. I had to do it once - my first fit of the tool post thread was too tight. I had marked alignment of the part relative to the chuck, but of course I needed to reset the tool in the thread. Easy as pie - between the cross-slide and the compound I was able to adjust the tool to just kiss the right hand face of the thread. I was able then to advance my spindle by hand to make sure I was tracking right, and got off another couple of thou to a perfect fit.
No worries, you did great! Ya, a few mistakes along the way but a mistake isn't a mistake unless you don't learn something from it. You learned plenty and prolly way faster than you would have without them.
Finish is its own art. Tool type and shape (a whole course of its own), surface speed, feed/cutting depth, material (both cutting tip and part), etc etc etc etc etc all affect surface finish.
For threads, the four most important things are a sharp tool, the right tool, the right speed, and to get the 29.5 degree compound advance angle right.
For math guys like you, the way to look at the 29.5 is to realize that it is designed to shave the right side of the thread groove just a hair to keep it smooth while the main left edge does the majority of the cutting.
Well done!
What did you end up doing to get the thread depth right?
Finish is its own art. Tool type and shape (a whole course of its own), surface speed, feed/cutting depth, material (both cutting tip and part), etc etc etc etc etc all affect surface finish.
For threads, the four most important things are a sharp tool, the right tool, the right speed, and to get the 29.5 degree compound advance angle right.
For math guys like you, the way to look at the 29.5 is to realize that it is designed to shave the right side of the thread groove just a hair to keep it smooth while the main left edge does the majority of the cutting.
Well done!
What did you end up doing to get the thread depth right?
Thanks, and thanks for the help.
I did it the worst possible way. I eyeballed "close" - I knew the tops of the threads would basically come off, and I'd be almost at form. Then I tore down my setup, pulled the tool post and test-fitted, found it tight, then put everything back and chased the thread back on. I'd left myself an extra half-inch of theaded space to cut off when I finished, so I had some nice sacrificial threads to test the setup with. Second try fit perfectly, nice and snug.
Following up on my QCTP install - it's working well, except that it's *just* marginal for the height of my compound - with 1/2 tools I wind up 20 thou over center. So there was only one thing to do. Today's fun was chucking them up in the 4-jaw and taking 50 thou off the bottoms. I could probably have taken as much as 125 without affecting function. No more problem centering.
You did well. Some people fight with that if they are hardened very much.
Usually why this happens is people buy the tool post size based on lathe swing specified in catalogs. But the critical dimension is top of compound to spindle axis & some import lathes are quite a bit higher by comparison.
Usually why this happens is people buy the tool post size based on lathe swing specified in catalogs. But the critical dimension is top of compound to spindle axis & some import lathes are quite a bit higher by comparison.
I followed the recommendation of the tech at BB. I don't regret the purchase, but the service is a bit off.
You got Accusize stuff at BB?
I did break a few inserts until I figured out depth of cut and speed.
Carbide inserts and interrupted cuts do not play well together. HSS is a better choice in those situations.
They call it BB4037 (iirc). I assume it comes down to what they can source.
Now you tell me!
Buy Quick Change Tool Post 6 - 12 Swing at Busy Bee Tools
Quick Change Tool Post Set (USA Style), Wedge Type Tool Post Sets consisting of 6 Pieces. Made of Steel. Each set consists of one Wedge type tool post and 5 different tool holders. Suitable for lathe center height 0.60 - 1.75" ( top compound surface to lathe centerline), such as: South Bend 9" &...
www.busybeetools.com
I'll be darned..... I'm going to have to go to BB and check this out. Accusize eh....... Same price as on Amazon.
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I recently helped another member deal with this same problem on his BB lathe. His compound is cast iron and has a raised section on it that the tool post sits on. We simply milled off a tenth of an inch from the compound. That way any new tool holders he buys will all fit just fine and he doesn't need to worry about turning down all his tool holders or any hardness issues.
We were also careful to assess the remaining thickness of the compound to make sure it wasn't weakened by cutting it down excessively.
It all turned out really well.
Yes, mine has the same step. I contemplated the same fix, but I'm not brave enough to swing my whole compound slide on the face plate. Until then, I'll keep taking smaller bites.
today I even went looking for some aluminium to try milling up some more holders, but Metal Supermarkets has decided to close Saturdays now due to staffing shortages. Which is, of course, the only day I can get out there given the day job.
Dovetail tool holders on a lathe? This should be interesting......
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There's so many threaded holes in them, I'm pretty sure I can set them up in the T-slots of my cross-slide. so it comes down to figuring out a collet for the end mills.
Surely you know someone with a mill......
Although shipping would prolly be required, you can certainly send it to me. I'll happily do it for you.
The good news is that your modified holders will still fit!
Lastly, don't be afraid of mounting the cross slide in your 4 jaw. Only a rough balance is required. And the back surface is plenty flat enough to mount it properly on the jaw flats or the chuck face. You only need to take a tenth off and that can be done slowly using a hss tool facing off 10 thou at a time. By using hss, you can cut slowly and the interrupted cut isn't that big a deal.
The real problem is mounting a cutting tool without a compound and tool holder...... LOL!
Has anyone figured out why the compound has that step on these lathes? I'm guessing it's an attempt to get more meat for the threads that hold the tool post.
I'll likely take mine apart today to measure the clearance between the feed screw and the casting, just to satisfy my curiosity.
I'll likely take mine apart today to measure the clearance between the feed screw and the casting, just to satisfy my curiosity.