[How do I?] Parting Blade Help

[zimm0who0net]

So it would seem I did a bunch of little things wrong here that contributed to the problems. Just curious, could someone measure the width of the bottom of their P1N blade. I'm guessing that all my problems were made much worse by having such a thin (0.012") blade bottom. I think I might retry with a different brand or perhaps a P1 or P2N blade.

 

[Bill C.]

I hate those parting tool holders. My ALORIS, yes, Aloris parting tool holder was not machines square to the back dovetail surface, I had to regrind the slot on my surface grinder to make it remotely usable. I am still having problems with it, as when I clamp the blade in it twists! So all my parts have a tapered cut. Ugh. I'll be making a new parting tool holder very soon.

From what I could see from photos online the holder appears to be a true pain in the neck. I used others that were not designed for common shaped blades. They look great but were difficult to keep perpendicular to the bottom groove and set-screws or clamp on top. I noticed your holder wasn't cheap to buy.

When I was parting small diameter parts I used a square HSS bit I ground down to about 1/8th of inch thickness by 3/4" so it would fit a standard tool holder.

 

[rick9345]

compound is extended too far, more RPM, feed with cross slide,tighten/lock carriage and snug gibs,heavy feed, small lathes very sensitive to parting,parting is a fairly heavy duty operation not suited to small lathes with no mass to absorb shock,adjustments need to be spot on. The smaller the lathe the bigger/wider the parting blade should be,kinda counter intuitive.

 

[higgite]

zimm,

I had overlooked that you said earlier that it is a P1N blade. Those are intended for small work, not necessarily for small machines, nor for parting 1/2” steel. Not saying it can’t be done, just saying. For reference, the P2 blade that I use is thicker at the bottom edge than yours is at the top. It is 3/32” thick and has successfully parted 3/4” steel on a number of occasions on the 7x14 lathe that I had when I bought it. That may be more blade than you want, but I suggest you go with at least a P1.

Tom

 

[tomh]

Zimm
Sorry if I sound critical in any way that is not my intention.
Here is what I am seeing from your photos. Your compound is extended to far, it should not extend past the bottom of the base of your compound, you are loosing rigidly there and risking snapping the compound off. If you look at the parting blade and holder it is hanging out in space to the left and and any pressure will cause it to bind and twist downward . There is no support there. This is a 101.21200 or a 101.100 correct ? The 6x18 lathes were basically made to use the lantern tool post holders where the tool would be in the center of the compound due to the small size and lack of rigidity. It will be in your best interest to use a saw to cut your part and then face it to size, This is my opinion only. These lathes were not made for that size holder and due to the size success will be iffy at best.
Hope this helps some
Tomh

 

[Dan_S]

I have a small lathe as well, so i'll throw my 2 cents in.

1. It might just be the picture, but the parting blade doesn't look square to the work piece. Mount a dial indicator, and take a reading off the blade, personally Id recommend being square to withing a .001 per inch or better. As other have mentioned the blade grove might not be parallel to the dovetails.
   
2. You need to minimize stick-out, specially on a blade as thin as this one. if you are parting 1/2" stock, don't let the blade stick out more than 5/16" - 3/8". The shorter the stick-out, the more rigid the set-up will be, and the better off you will be.
3. You need to be right on center height. It's hard to tell from your picture, but it looks low.
4. Grind the edge square to the blade. On wider blades you can get away with skewing the tip to leave the nub on one side or the other, but thin blades just don't like it.
5. Cutting fluid/oil is your friend. HSS blades like this are constant width, across the top of the T, so the deeper you plunge the more rubbing you will get. Cutting fluid helps as a lubricant and as a coolant.
6. Speed and feed is important. On my machine 8" I'd be spinning a 1/2" part as 600 rpm or so, and feeding as hard as the machine can take. I usually listen for the motor to load up and then I know I'm in the sweet spot.
7. Use the widest blade you can, it will help maximize the rigidity of the cut. On my machine, I use a P-2, anything narrower gives me grief.

About the tool holder.

1. The Frank Ford T grove modification helps, specially with wider blades.
2. make sure the bottom of the holder has a nice crisp corner as well, I've seen several that a small radius, most likely because the cutter being used to make it was getting old. The radius makes it hard to get the blade nice and vertical.
3. This style holder in PITA to change stick-out, because you have to change too height as well.
4. I really don't think this holder style works well in general, because it's applying all the clamping force at the front of the blade.

 

[brino]

I think it's been nailed above.
All my parting troubles disappeared when I went to a wider parting off blade.
It sounds backwards; like you'd want to minimize blade width to minimize cutting force, but believe it rigidity is everything here.
-brino

 

[zimm0who0net]

Seriously you guys, this forum has been fantastic. I see a bunch of little things I can try differently. Biggest one is to just buy a thicker blade.

Your compound is extended to far, it should not extend past the bottom of the base of your compound, you are loosing rigidly there and risking snapping the compound off.

Actually, believe it or not, the compound is retracted all the way to the back end. I did that on purpose because I don't have a lock on the compound so I wanted it against the back stop so it couldn't back-drive. The tool post does hang way off the side of the compound. That's a function of the size of the compound rest and and the comparatively large size of the toolpost. I did have the toolpost in the middle of the rest, which I see now is a mistake. I moved it clear to the farthest end so now the cutting tools/blades end up much closer to the rest.

This is a 101.21200 or a 101.100 correct ?

Technically it's a Atlas Mk2 3950, but that's more-or-less exactly the same as a 101.21200

Your tool holder looks very similar to the Tormach parting tool holder from LMS that I have, except mine holds the blade horizontal, with no rake, and has a “T” on the end of the model number, 250-007T.

This style holder in PITA to change stick-out, because you have to change too height as well.

Ain't that the truth. This is EXACTLY the Tormach from LMS, but the recommendation for my lathe from LMS is the 250-007 over the 250-007T because I've got a bit more clearance between my rest and the centerline of my spindle than most of the 7" mini lathes that are out there. Soooooo regretting that now.

...P1N blade is just too thin at .012”. Did you double check that measurement?

Yep. It's that thin. Still wondering if maybe this blade was defective, but I can't find any info online on how thin the bottom of a P1N is supposed to be. Thinking about contacting Shars and trying to get them to replace it with a thicker blade. Heck, it's so thin that I can snap pieces of the blade in half with my fingers

Maybe reaching for straws a little with this question, but do you lock down the carriage when you part off?

Nope. Didn't lock that down. Someone else mentioned that. I do have a dial indicator on the slide and I don't believe it moved, but I certainly should have locked it.

 

[Tozguy]

Am learning a lot from reading this thread...thanks everyone.
About turning upside down (or backwards) with the 007 holder, if you mount the blade upside down in the holder doesn't that reduce the top rake angle and increase the relief angle? Is that why it would work better than when upright? Or do you regrind the tool for the different position?

 

[higgite]

Toz,

I'm just speaking from my experience with a Tormach QCTP and tool holders like zimm has. Others may see it differently. You're right about the angles changing if you turn the blade over in a 007 holder. I could be wrong, but I think you would have too much negative rake for it to work.

Another monkey wrench in the works with an upside down blade in either the 007 (angled) or the 007T (horizontal) tool holders is getting the cutting edge aligned with the center of the spindle. It may be possible, but even so, the holder would be protruding out the top of the tool post such that the tool post would have a tenuous grip, at best, on the holder.

Tom