tooling for cutting off acme thread?

[shootingarts]

These numbers may or may not be exact as I am working from memory but I wanted to post this question for thought before heading out to the doctor's office for some work on me this morning.

A job that has to be done hundreds of times a year is turning 1-1/4" of one end of a 1"-5 acme threaded rod down to 3/4" inch. A square shoulder at the start of the acme thread and a small chamfer on the end of the shaft completes the job. Currently a standard carbide insert and tool holder are used to make an interrupted cut until the threads are removed and then the same tool is used to make the finish cuts. Trying to hold production shop times is making heavy work for the 16x60 lathe being used and times still aren't satisfactory.

I believe I can speed up the work somewhat by making more lighter cuts at higher speeds but I also keep thinking about some change of tooling to change the intermittent cut into a continuous cut. Grinding isn't an option and space and lack of enough justification for purchasing a bigger lathe prevent just throwing more size and horsepower at the problem. Subbing it out hasn't proven feasible either so I am left with a change in cutting speed and depth or a tooling change to hopefully lighten the load on the machine and increase the speed of this job. Any thoughts on tooling?

Thanks,
Hu

[widgitmaster]

Not sure if you are using a multi-tool turret, or a standard Aloris type toll holder system.
Either way, try using a cobalt tool the full length of the turned area, and plunge straight in until you reach the thread root.
The cobalt tool should have a nice chip breaker groove to curl up the chips.
The 16x60 lathe has more than enough power to accomplish a massive cut like this, so let the machine do ALL the work!

Do this to all then turn as normal!

Widgit

[shootingarts]

Originally Posted by widgitmaster Not sure if you are using a multi-tool turret, or a standard Aloris type toll holder system. Either way, try using a cobalt tool the full length of the turned area, and plunge straight in until you reach the thread root. The cobalt tool should have a nice chip breaker groove to curl up the chips. The 16x60 lathe has more than enough power to accomplish a massive cut like this, so let the machine do ALL the work! Do this to all then turn as normal! Widgit

I am using an ALoris type post. I have the turret post that came with the machine also but the quality is lacking.

Just verifying, you are talking about using a tool with a very wide face to plunge cut all of the thread off at once? I would have thought that chatter would be an issue since the area of the acme thread being cut would total around a half inch wide. I'm thinking a very stubby tool and see what happens though, if chatter is an issue maybe two plunge cuts or it may not even be an issue, I won't know until I try. The lathe is a Jet, a good bit of horsepower but not as stiff as an old machine.

Thanks very much for the reply and have a very merry Christmas!

Hu

[widgitmaster]

Yes, it may chatter, so keep the RPM down, usa a flood of coolant, and keep the part & cutter as close to the chuck as possible for rigidity.

Then slowly increase RPM & Feed untill it is most efficient!

Have fun & Merry Christmas!

Widgit

[shootingarts]

Originally Posted by widgitmaster Yes, it may chatter, so keep the RPM down, usa a flood of coolant, and keep the part & cutter as close to the chuck as possible for rigidity. Then slowly increase RPM & Feed untill it is most efficient! Have fun & Merry Christmas! Widgit

Thanks!

I'll give it a try when I get a chance.

Hu

[sluggo]

That should only be about .1 a side, have you tried to lower your chip load and take the interrupted cut in one pass.

[shootingarts]

Originally Posted by sluggo That should only be about .1 a side, have you tried to lower your chip load and take the interrupted cut in one pass.

Sluggo,

I'm not sure what you are telling me here. I have tried coming in from the end and cutting all of the thread off at one pass and as we normally cut, bringing a tool across the rotating face. The problem in a nutshell is that this is a process that has to be done over and over for a flat rate per piece. Easy enough to do at a slow pace but reducing the time per shaft is the issue. The real issue is that we aren't charging enough for the job but there isn't any help for that.

One alternative that I haven't tried is a tool with a cutting face just wide enough to engage several threads so that it is never an interrupted cut when cutting across the threads. If I kept the load even I might be able to take a more aggressive cut. I'll have to break out some scrap when I get time and test everyone's ideas.

Hu

[sluggo]

so you have tried cutting along the axis at a depth of cut just deeper than the thread depth? The maybe you can plunge them off faster like widget master is saying. You might not even need a tool that is 1 1/4" wide, maybe a carbide grooving insert that is .5 wide and do 3 plunges at a faster rate.

[widgitmaster]

The 1010 or 1018 steel rolled into a deep acme thread has a tendency to work harden, and with the interrupted cut is very abusive on carbide. Even with C6 or C7 grade!
Also carbide is crystalline, and that does not help. Therefore, using a solid Cobalt tool bit in one tool holder to plunge straight in removing all the intermittent threads, will allow you to finish all the diameters with another tool in another holder.

The Cobalt should cut right thru the steel threads and probably start chattering when engaged in a the full cut at the root of the threads.

I have been turning acme threads on my 13x40 lathe for a year now, and have also seen tools burn up after 2 or three parts. That's when I setup one tool specifically for ruffing the diameters, and one for finishing.

One last note would be to tighten the gibb's on the compound and cross slide, as any deflection during the intermittent cut is resonating the carbide tool to it's limits causing it to break down.

Widgit

[sluggo]

is it rolled? maybe use a tool holder with a 45degree insert and take it all in one pass, that way you thin your chip there for using less power, allowing you to kick the feed up a a few notches.

[shootingarts]

Originally Posted by sluggo so you have tried cutting along the axis at a depth of cut just deeper than the thread depth? The maybe you can plunge them off faster like widget master is saying. You might not even need a tool that is 1 1/4" wide, maybe a carbide grooving insert that is .5 wide and do 3 plunges at a faster rate.

This machine is equipped with a good DRO which makes it easy to run in and leave just a ghost of thread rather than cut them completely away maybe avoiding chatter. Then I can swap tools to a narrower faced one to cut into the continuous cutting part of the shaft on the next pass. I do intend to try both the very wide tool and a somewhat narrower tool with the plunge cuts. I have another lathe apart I need to get together first but I think Widget's idea of tightening the gibs is excellent too. This machine does mostly rough work and hasn't been adjusted out in years.

To reply to your later post also, this is a rolled thread and there is considerable work hardening. The 12' 304 stainless round bar makes about 12.5' of acme threaded bar. That is a lot of moving around. Not sure if I can hang a 45 degree insert far enough out to try a cut like you are talking about but it would be worth a try. Worst comes to worst it wouldn't be the very first insert I have broken!

Thanks Again,
Hu

[snowshovelbmx]

I think that you may have forgotten to mention that the material is 304 SS that changes things a little bit as it probably is like you say considerably work hardened.