PM 1236 tool post issues

[qualitymachinetools]

Hey Blackhawk,

If the holder is crooked, I can swap it out, that is not a problem at all.

But the problem you are having is not caused by the holder, there is no way. Especially not with a regular turning insert, or a HSS Ground threading too.

POSSIBLY on a parting or grooving tool, but thats about it.

Can you post a pic of the threads and what it is doing?

The Aloris posts are great, yet. But don't spend the money on the Aloris just to fix that, that will not do anything, that post that came with it will work fine.

If you can sent a close up picture of the tool, the threads, or even a video of the process that we can watch, we can help you out a bit more to get you going.

 

[Blackhawk]

Mat,

ill post a video in a few days, gonna be 72 here in fredericksburg today so ill be out soaking in the sun

lanham

 

[Blackhawk]

[video=youtube_share;eFLn_0QVw6Q]http://youtu.be/eFLn_0QVw6Q[/video]


It's cold again so I'm back at it, positive results, thanks so much for everyone that helped.



lanham

 

[darkzero]

Good to see you were able to get good threads, congrats.

If the shims are working out for you then that's all that matters. One thing that came to mind watching your video. Tool blanks generally have sharp corners (very little radius). All my indexable tools have a moderate radii on the shanks. I'm wondering if the slots on your holders aren't machined with a perfect 90° and may have a small radius in the corner of the slot? If so that could be the cause of your rocking/gap issue. Probably not the case but just a thought.

Some guys will mount tool blanks slightly pulled outwards for various reasons. You can always turn your tool post to square up the 60° point to the work. I still have the same holders you have, I'll check the slots on them tomorrow to see if I get the same results.

It's better to use the tool holder without the v-groove for flat shank tools. The holder with the groove is for holding round shanks, mostly used for boring bars.

 

[Radarguy]

If you truly want to square the bottom of the holder slot it would be easy enough to get an end mill of the appropriate size (like 1/2") and chuck (collet if you have them) into the lathe and cut a new bottom.

Russ

 

[Buggy Chief]

Great write up!! So being new, what is the angle of the tool post on compound carriage?

The first indexable tool you showed is using a CCMT 32.5 style insert, I use the same tool quite often with CCGT inserts. Not sure if you actually did try using that for threading but it's only good for facing & turning since it's an 80° diamond shape insert, not good for 60° thread forms.

If you are threading soft aluminum or finer threads on steel, instead of the modified flank method (feeding with compound set at 29-29.5°), try threading with just feeding the cross slide straight in. The modified flank method is the better way to thread (arguably) since it's less wear on the cutter, less tool pressure, etc., but if you're not threading a coarse thread you can get away with feeding straight in with the cross slide on a lathe this size. Align the tool bit tip with the work using a fishtail & give it a try.

You mentioned jagged/sharp threads. If you were using the modified flank method to cut threads, that's usually a good indication of the compound angle set incorrectly. This is a common mistake with Asian lathe owners new to threading. The compound must be set 29-29.5° off the cross slide or 61-60.5° off the spindle axis.

Many (but not all) Asian import lathes do not come with a full protractor for the compound slide like older American lathes do. Most of them indicate 0° when parallel to the spindle (like the PM1236 does, I have the same lathe). So if you set 29° on the scale you are at the wrong angle for threading. You will need a protractor to set the correct angle for threading as the scale on the compound slide is useless for that.



This is what 29.5° looks like using the scale, incorrect for external threading.

This is what 29.5° looks like for threading.

As you can see the scale is useless for that on the PM1236.

I use a preset slide bevel to set the compound for threading.

 

[tmarks11]

For cutting threads, you want the compound to be 29.5 degrees off aligned perpendicular to the workpiece. Which on most lathes is at 60.5 degrees on the protractor (as read from the front of the cross slide, or 29.5 degrees as read from the side of the cross slide... where there is generally no mark inscribed).

You want the tool post and tool bit to be lined up exactly perpendicular to the workpiece. You can achieve that with a small machinist square, or use a DTI fixed to the headstock and run the cross slide in and out with the DTI running on the tool bit edge. Adjust it until you get (almost) no DTI deflection (a few thousands isn't going to matter).

EDITED: Tom points out that 59.5 + 29.5 leave me a degree short of perpendicular.

 

[Buggy Chief]

thx

 

[Muskt]

BC,
Below is a link to my site where I describe the way I set up the compound for threading. Granted it was on a 9x20; however, the techniques are the same.
I hope it is of some value to you.

http://www.akpilot.net/Threading Setup/Compound Setup For Threading.html

Jerry in Delaware

 

[Buggy Chief]

Excellent write up Jerry for a beginner like me. I feel like I have enough to get started. Excellent forum!!