Removing "Snipe" from Interrupted Cuts?

[markba633csi]

If that spindle has sleeve bearings there is almost certain to be some play there- that could be the culprit
I'm not that familiar with the 109 headstock

 

[RaisedByWolves]

Fortunately I have a late model 109, so it’s got a 1” spindle instead of their 1/2” from earlier models. That said, I hadn’t considered the spindle as contributing to the issue. I suppose either way, this little lathe can only do so much so it is what it is. I guess I’m just trying to figure out how to minimize this issue for future reference if I were to have another situation like this again. Hopefully a milling attachment and other means will be in my future to help and I won’t need to make any similar interrupted cuts like this when the time comes, but who knows.

I’m including a couple pictures to illustrate what I’m talking about. Ha, I thought I did ok with the finish until I took these!
View attachment 516423
View attachment 516424


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If you keep leaving the T handle in the chuck like that its going to bite you sooner or later.

As to your issue, Id start by tightening up your gibs. The machine may have wear that you cant dial out, but this would be a good start. You can lock the gib screws on the compound down tight when not using it and probably eliminate a large percent of that right there..

 

[markba633csi]

Indeed, if one is going to put an eye out- don't advertise it

 

[evergreenblue]

Thanks, everyone.

Wow, I can't believe I actually left the key in the chuck in that photo! I had just removed the part to take the picture - I assure everyone I do a check before turning anything on, but that's a good call-out to just never let it leave my hand in general. I truly do appreciate that call-out.

Regarding the suggestions, I was watching as I was cutting, and couldn't see any actual movement on the saddle or compound, and I tightened up the gibs for the compound and cross to just allow stiff movement. Good tip on tightening the compound all the way though. I'll have to see if I can't get a handle on where that vibration is based on the recommendations and see what I can do. It's an old lathe, but it's what I got so I'm going to try and figure out how to get the most from it. I just measured the part and those "snipe" areas and have an error of 0.1-0.22mm depending on which cut is measured. I'm planning on lapping it a bit to correct this for this part, but will probably use a piece of scrap to replicate this after I check everything over. I'll report back!

 

[RaisedByWolves]

Thanks, everyone.

Wow, I can't believe I actually left the key in the chuck in that photo! I had just removed the part to take the picture - I assure everyone I do a check before turning anything on, but that's a good call-out to just never let it leave my hand in general. I truly do appreciate that call-out.

Regarding the suggestions, I was watching as I was cutting, and couldn't see any actual movement on the saddle or compound, and I tightened up the gibs for the compound and cross to just allow stiff movement. Good tip on tightening the compound all the way though. I'll have to see if I can't get a handle on where that vibration is based on the recommendations and see what I can do. It's an old lathe, but it's what I got so I'm going to try and figure out how to get the most from it. I just measured the part and those "snipe" areas and have an error of 0.1-0.22mm depending on which cut is measured. I'm planning on lapping it a bit to correct this for this part, but will probably use a piece of scrap to replicate this after I check everything over. I'll report back!

Have you checked your spindle for deflection?

 

[evergreenblue]

I haven't, no. I'm ordering a dial test indicator and will check everything suggested. I'm assuming I should not only check for runout, but also check for actual movement in different directions with force as suggested. I'm also assuming that the chuck wouldn't be a good reference due to variation from the spindle threads? Any suggested procedures would be appreciated.

 

[extropic]

You don't have to remove the chuck to do the survey. The poor finish has nothing to do with runout and, because the workpiece is rectangular, you're using a 4 jaw chuck. The intention of the survey is to look for what is soft, insecure and/or poorly adjusted and causing the lack of rigidity in the setup.

I'm wondering if the lathe has ever been crashed in a way that has bent the compound slide? I once bought a used lathe that had the compound bowed down from being well extended and crashed into the chuck jaws. The bow in the dovetail resulted in not being able to achieve full range of travel with proper gib adjustment. Therefore, until the compound was straightened, if I wanted full range of travel the gib would be too loose for a lot of the travel. I imagine that sloppy compound could result in your finish issue. Just wondering.