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

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Aaron_W

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#1
I have the standard front mount cutoff tool (3002) that came with my lathe. I understand the potential advantages of the rear mount but wondering if there is any reason to get the dedicated rear mount cut off tool (3018) vs the rear mount spacer block (3016) that converts the front mount cutoff tool to a rear mount.
I can't imagine there are that many situations require both a front and rear mount tool at the same time, and other than the spacer block potentially being a little less solid, it seems like the spacer block would be preferred for the added flexibility and being cheaper if one already has the front mount cutter.

Any flaws in this logic?
 

mikey

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#2
Do yourself a big favor and make your own rear mounted parting tool post. Each lathe has its own spindle centerline and this determines how well the tool cuts. This is a simple project that a new guy can do. If you need guidance, PM me.
 

DHarris

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#3
what Mike said! Rear cutoff works great on my Sherline!
 

tweinke

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#4
Someone should post a picture of there rear mount parting tool because I'm sure it would be a good reference for others.
 

mikey

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#5
Sure, here you go:

IMG_5298.JPG IMG_5300.JPG IMG_5303.JPG

The cutting edge is on the exact centerline of the lathe spindle. 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.
 

ddickey

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#6
I'm planning on doing this also. I have a Phase II piston type QCTP that I'm not using and thinking about integrating that into the rear mount. Will probably be mounted on a 2024 aluminum block. Not sure how I'm going to mount the block on my cross slide, whether I tap or drill and use a nut on the bottom.
 

Aaron_W

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#7
I still haven't got used to the idea that I can make stuff...

Mikey, I'm still in the midst of rearranging a new shop. The addition of the mill and grinder has caused some adjustment. Once I'm set up I will follow up on your offer. It probably seems easy, but I will need some help finding the right height for the cutting tool.
 

Bob Korves

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#8
It probably seems easy, but I will need some help finding the right height for the cutting tool.
Chuck up a piece of rod and face it. The middle of the bullseye on the face of the work is the correct height.
 

T Bredehoft

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#9
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 .
 

mikey

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#10
I still haven't got used to the idea that I can make stuff...

Mikey, I'm still in the midst of rearranging a new shop. The addition of the mill and grinder has caused some adjustment. Once I'm set up I will follow up on your offer. It probably seems easy, but I will need some help finding the right height for the cutting tool.
Yeah, let me know when you're ready.

It is critical that the point of the parting tool be on the exact centerline of the lathe, and every lathe is different. If it is too high, it won't cut. If it is too low the tool can dig.

The best way to get center height is to turn a piece of something - steel, aluminum, brass. Turn to get a consistent diameter and finish, then measure the distance from the mounting surface where your parting tool post will sit to the top of the rod you turned. Be as concise in this measurement as possible; I use a height gauge. Then measure the OD of the turned piece, subtract 1/2 that OD from the height gauge measurement and you have your spindle centerline.

A rear mounted parting tool is used upside down. The bottom of the slot that holds the parting tool must be at the distance you found in the step above. You cannot be above that measurement but you can be below by maybe a thou or so but try to get it exactly right. A sharp tool positioned this way will not dig, chatter or do anything else but cut.
 

mikey

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#11
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?
 

T Bredehoft

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#12
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.
 

Jimsehr

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#13
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.
 

j ferguson

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#14
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. ??
 

ddickey

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#15
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.
?
 

mikey

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#16
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.
 

ddickey

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#17
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.
 

mikey

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#18
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.
 

ddickey

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#19
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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