Parting Trick

mikey said:
I should write up my tool height gauge when I have some time. It is simple and very nearly foolproof because it has no moving parts. When I have time.
Click to expand...

Please do. I still don't quite follow your description.

I got my P1 parting tool and it's more bad news than good news but mostly the tool holder problems.

First of all, it bottomed out about .010" above or below center, depending on how it was used. The fix was easy, I just milled about .050" off the top surface and it was good to go.

Second problem was that when I tightened the screws that clamp it in, the tool would shift, sort of a tilt. Obviously the bottom of the holder was not square with the side so, back to the mill to square that up.

The QCTH is that $30 aluminum job and it's other quirk is that the dovetails are as cast with no machining and are very sloppy. With a shim on one side, it locks pretty well so I give it a pass at this point.

I spent a good deal of time with a 1.5" aluminum bar cutting fender washers and finally got it to work well enough in the upside down mode but it was pretty tedious feeding it. I really miss my old lathe with power cross feed.

Next, I tried a 5/8" mild steel bar and it was pretty hopeless at any speed.

I am thinking that 3/32" is just beyond this little machine so I am going to order a P1 tomorrow and hope that's the problem.

What I really do not understand is just what is vibrating when it chatters. It's as close to the chuck as I can get it and the tool extends no more than half way into the part.

js
 
@jschmidling, what kind of lathe are you using? Is the parting tool held at an upward angle? How precise did you get the tip on center? Did you mount the tool upside down and were you then running in reverse?

A pic of your set up would really help.
 
Parting. Aaaarg!!! I am parting challenged. Most of the time I end up resorting to my hacksaw to finish the part off and then face off the rough edge. I am ready to make a backside parting tool holder (BPTH). I have some 2x1.25 1018 bar stock on hand for the base and some round stock that I could turn down for the post. The cross slide on my craftsman lathe does not have a "T" slot nor any holes to mount anything. I think that the only way I could make a BPTH is to have it fit in the dovetails on the saddle. Then how do I connect it to the cross slide to move it. In looking at Mikey's parting tool holder I thought instead of trying to attach the BPTH to the cross slide why don't I put another cross slide nut on the lead screw and attach the BPTH to that. Here is what I am thinking.

Backside parting tool holder 001.jpg

Backside parting tool holder 002.jpg

The post is the same diameter as my norman style QCTP and I would use the tool holder for the parting blade that I have already made. Turning the lead screw would move the BPTH in or out and I could use the power feed.

What do you think of this?
 
mikey said:
@jschmidling, what kind of lathe are you using?
Click to expand...

7 x 12 Mini, Wen brand

>Is the parting tool held at an upward angle?

No.

>How precise did you get the tip on center?

Within a mil? Split the tip on my brass tool described up thread.

> Did you mount the tool upside down and were you then running in reverse?

Yes to both.

>A pic of your set up would really help.

Attached two. Note my last attempt was to experiment R-L relief and it made no difference other than the obvious.

Jacklathe8.jpg
 

Attachments

  • lathe6.jpg
    lathe6.jpg
    42.2 KB · Views: 24
I can think of a few reasons for this set up not working well. Parting depends on a very rigid set up so if the tool post itself is not solid then that causes issues; how rigid is the tool holder held in the post? The tool holder must hold the blade perfectly vertical or the blade will steer; is the body of the blade flat up against the tool holder's blade slot? The tip of the cutting edge must be on the dead center of the lathe centerline, not within a mil; the smaller the lathe, the more important this becomes. I cannot tell if the blade is sharp and deburred but I assume it is, right? Are the gibs properly adjusted?

Another idea is to make a rear mounted parting tool post and mount it at the rear of the cross slide. You would need to drill and tap a hole but that wouldn't be a problem. Might want to consider it if you plan to stay with this lathe. I suspect it will solve a lot of problems for you.
 
I'm going to need to root around my stock shelves. I know I have steel that will work, not sure about aluminum.
 
mikey said:
Another idea is to make a rear mounted parting tool post and mount it at the rear of the cross slide. You would need to drill and tap a hole but that wouldn't be a problem. Might want to consider it if you plan to stay with this lathe. I suspect it will solve a lot of problems for you.
Click to expand...

I am getting soggy here and think I can summarize by saying I am doing the best that I can with what I have to work with.

I would love to build a rear mounted tool holder but I need some better pics or drawings of such a thing to under stand it and how it would be mounted ........

Just found your blog and when I saw the word "aluminum", you lit my fuse. My "mill" is not up to machining steel but it works well enough on Al for this project.

I need time to digest this so will get back when I come up for air.

Thanks,

Jack
 
jschmidling said:
I would love to build a rear mounted tool holder but I need some better pics or drawings of such a thing to under stand it and how it would be mounted ........
Click to expand...

Have a look at the design I posted on MachinistsBlog (not my blog, by the way) and make one to fit your lathe's centerline. It would have a ledge that butts up against the side of your cross slide. A hole would need to be drilled and tapped in the bed of your cross slide to accommodate a bolt that goes through the parting tool holder to hold it to your cross slide. Care needs to be taken to ascertain the exact height of your spindle centerline as this determines the height of the blade slot. Otherwise, nothing else is critical.
 
mikey said:
Have a look at the design I posted on MachinistsBlog (not my blog, by the way) and make one to fit your lathe's centerline
Click to expand...

You sold me on rear mounting but with my relentless crusade to KISS, I made "a few changes" also in keeping with my now very humble shop facilities.

The attached pic is a model in wood to test the concept. I ordered a 1/2" x 2" piece of aluminum bar stock and some proper hardware for the real thing.

Although not as rigid as a solid block, I think it will be an improvement over what I have been trying to do in front with the compound slide and marginal tool post.

The only milling required is the shelf for the tool itself and possibly squaring up the cut ends. If the washers don't work, I will make a proper hold down bar.

Depending on your point of view, it has the "advantage" of being tweaked in all axes.

Thanks for the ideas. Will report back when made.

Jack
lathe10.jpg
 
You must log in or register to reply here.
Back
Top