Advantage to Rear mount cutoff 3018 vs 3016 rearmount spacer block?

Re: Rear mount cutting tool, I went to the trouble of making a new cross slide base for my Atlas Clausing MK2 620 lathe. put a rear mount cut off tool on it. It worked fine until it somehow jammed and lifted the back of the cross slide about an inch. The problem could be the plastic gib on the cross slide. I've been thinking about making a bronze gib to take it's place, haven't done it yet .

Tom, I wonder if the center height of your parting tool might be a tiny bit off?
 
the center height of your parting tool might be a tiny bit off

Good catch, Mike, it wasn't a tiny bit, .050 or so low. I engineered the thing, never checked to see just where it was. Back to the shim shop.
 
Rear tools also let you time tools . I will have to make a set up and take I pic of how
To do this. Done all the time when doing production parts. Say you want to face a part in front tool post and time a groove in the back to hold a very close length from face of part to groove.
 
Rear tools also let you time tools . I will have to make a set up and take I pic of how
To do this. Done all the time when doing production parts. Say you want to face a part in front tool post and time a groove in the back to hold a very close length from face of part to groove.

"time" tools? New term to me. ??
 
Top two screws hold the blade in place. The center screw holds the post to the bed with a t-nut. The ledge registers on the edge of the cross slide so the tool cannot move. Parts with no issues at all.
Mikey,
the ledge is to keep the block from turning? There's not much force trying to turn the block is there?
The reason I ask is I also put a register on the edge of mine. I did mine more for reference to the work. I also put a dowel pin under my toolpost but wondering if it will be necessary as the side forced should be small.
?
 
Like you, I use the ledge to get the blade perpendicular to the work automatically. It also makes it nearly impossible for the tool to move once the T-nut screw is locked. It takes all of about 10 seconds to get the tool onto the cross slide bed and I'm cutting.
 
I'm almost finished with my rear mount. Took some test cuts and man did it squawk and chatter. Played around with the height adjustment and now seems much better. For some reason seems much more finicky. I will sharpen the blade as well today. Time will tell if it's any better. My FoR tool mounted in the front performed very well though. I thought it would be nice to have it in the back and my plans were to keep it mounted all the time. Unfortunately it is a bit bulky and somewhat dangerous to keep it mounted will you're turning as it could go into the chuck. I used 2024 for the riser and cut a t-slot into that and mounted a QCTP. Was thinking about trimming the block I think I'll just leave it as it.
I think not using a QCTP would be much better. Something like what Mikey did integrating the block and holder as one. I was concerned about center height and thought I may thread from the back once in a while.
 
I think not using a QCTP would be much better. Something like what Mikey did integrating the block and holder as one. I was concerned about center height and thought I may thread from the back once in a while.

In my opinion, a purpose-made rear parting tool post is the best idea. It needs to be solid and the blade must be on the exact centerline of the spindle but if you get this done the tool will part really well. If you make the post register so the blade is automatically perpendicular to the work when you mount it, it speeds things up significantly. Once done, stickout of the blade and speeds are not really important - go fast, slow, or medium speed and it will cut. Folks also think that as material OD increases, so must the parting blade thickness but I've found that a P1 blade will easily cut most stuff that fits in my chucks. A rear mounted parting tool will make parting so easy that you'll wonder why you would do it any other way.
 
Mike,
I agree. I did sharpen my blade and tried some test cuts, works great. I may redo mine in the future.
My blade is a T type 3/32" wide.
 
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