Cutoff Inserts & Blades?

================= Cut-off [parting-off for our UK readers] is one of the harder lathe operations.

I question if you should be using carbide and carbide insert tooling. These are normally of benefit only for high speed machines with lots of power and great regidity in a high volume production situation. I would at least try using a HSS [not cobalt] blade. Cobalt is not suggested because it is more brittle, and harder to grind. Unless you are in production or are having excessive wear, M2 HSS will generally prove more satisfactory.

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One 'trick" that is frequently used with the smaller machines is a rear mounted cut-off toolnholder with the blade mounted "upside down." This seems to greatly improve the rigidity and helps keep the cut free of chips. As a class project we made one of thes for our Emco Compact 10 see

Good luck.

Unka' George (George McDuffee) .............................. Only in Britain could it be thought a defect to be "too clever by half." The probability is that too many people are too stupid by three-quarters.

John Major (b. 1943), British Conservative politician, prime minister. Quoted in: Observer (London, 7 July 1991).

I've wondered about this, but I figure carbide would be best for cutting SS. I think I have soem HHS blades around somewhere, but still only the

I've wanted to make one of these for a while, but haven't had time. Several photos of the final result seem to be missing from the web site.

I've been using "Cool Tool II", which has worked well on SS for a number of other projects. It's not nearly as messy as the black stuff.

Thanks for the suggestions.

Doug White

I've recently converted from 1/2" high HSS parting tools to an Iscar insert and holder of the same size as you mention (25mm high with 2.2mm inserts). This is in a Myford ML7 that is smaller than your Super 11. Thus far the largest I've parted off with it was 2 1/2" MS and 1 1/4 4140 so I don't know how I'd do with SS. I did manage to bury the tip a couple of times in the large section until I got the speed and feed at a happy level for the tool. After that, I've found it to be far better than the HSS tool.

It may be worth starting the job with the tool only stuck half or the required distance out of the holder, then loosening the clamps and knocking it further out halfway through the cut. This will make for much less stress on the topslide, tool holder and you.

No. A thicker blade will be stronger only in proportion to the thickness, and the cutting forces will rise in proportion to the thickness as well. Mean while, the tool post and top slide are the same.

I'm using Iscar at the moment. But Kennametal, Dorian, Widia Valenite, anyone else that fits will probably do exactly the same job.

Shop around, the insert prices seem to be higher than for normal turning inserts, but I've only got four so far and haven't broken any yet. So I don't know if it's worth buying in larger quantities to get discounts.

Mark Rand RTFM

Doug, I don't know anything about SS, I do know how much better I like cutting off with an insert tool.

I've been buying inserts (in pretty small quantities) from this place:

Steve

Doug White wrote:

============ Production carbide tooling tends to be negative rake. This works great on the higher power rigid production machines, but in many cases the smaller home shop lathes lack the rigidity and power.

HSS blades will let you grind in positive rake, [4 degrees is a good starting point] or if you have a die grinder with a 1/4 or

FWIW -- you will need one grind for brass [and other "grabby" material] and one for everthing else. You can grind one end of the c/o blade for brass and the other for steel if you are short of tools/money.

Unka' George (George McDuffee) .............................. Only in Britain could it be thought a defect to be "too clever by half." The probability is that too many people are too stupid by three-quarters.

John Major (b. 1943), British Conservative politician, prime minister. Quoted in: Observer (London, 7 July 1991).

I learned to run a lathe running a 20" American Pacemaker. Cutoff was trivial on that machine, just powerfeed the tool in, never worry. On my 9" South Bend, cutoff was a giant bitch to say the very least. However, I made 2 projects, the T-slot cross-slide table and the rear cutoff toolpost, both from Metal Lathe Associates, and now it's quite manageable. I sold my insert tooling, this works

The best writeup on parting off I've seen is in the late George Thomas's book, "The Model Engineer's Workshop Manual". He was also an advocate of rear-mounted cutoff tooling, mounted upside down. He also has a very good writeup on how to grind HSS cutoff blades - no, grasshopper, you should NOT use them as they come from the manufacturer. Although you can get away with it sometimes ..

GWE

Steve Smith wrote:

top posted

Metal lathe associates website is at

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Unka' George (George McDuffee) .............................. Only in Britain could it be thought a defect to be "too clever by half." The probability is that too many people are too stupid by three-quarters.

John Major (b. 1943), British Conservative politician, prime minister. Quoted in: Observer (London, 7 July 1991).

George any idea when the missing pictures will be posted in the above link? ...lew...

First, you have to burry chicken guts in the back yard at midnight on the night of a full mood while burning black tallow candles. Then you need perfect rigidity, unlimited horsepower and perfectly ground and profiled tooling. Without those things, use a bandsaw.

The standard Aloris AXA cutoff holder has some rake built in so you don't need to grind the blade. Unfortunately, that's the one with the 1/2" high blade that I've already lost on end on.

Doug White

============================ I will get the camera out and see what I can do.

Almost all the other pictures on the wep page were taken with a high end Sony digital camara that the school has. I retired, and will be using a cheapo 640 X 480, so the quality may not be as good.

Unka' George (George McDuffee) .............................. Only in Britain could it be thought a defect to be "too clever by half." The probability is that too many people are too stupid by three-quarters.

John Major (b. 1943), British Conservative politician, prime minister. Quoted in: Observer (London, 7 July 1991).

snipped-for-privacy@alum.mit.edu (Doug White) wrote in news:V-udnY2Ta9cPjdDYnZ2dnUVZ snipped-for-privacy@rcn.net:

Even on a big powerful CNC lathe you would try to avoid cutting off 2" diameter bar. You are almost always better off cutiing balnks slightly oversize on a say, then facing to length. But, sometimes the part configuration doesn't allow for that. So...

One trick that I've used on production parts is to use a wider tool to cut down to a 3/4" diameter, then change to the narrow tool. In any case you will have difficulty using such a narrow tool, plunging an inch deep.

The other thing I didn't see in any of the posts was whether or not you are using the power feed on the cross slide. Cutting off by hand is extremely difficult unless you are using a lever operated cross slide. For stainless and a 3/32 wide tool you should be feeding at .002" per rev. Assuming 303 you should be running around 400 RPM.

The tool should be set dead on center or slightly above. Check the squareness of the blade to the work with a DTI or at the very least a good machinist's square.

Cutting off with the tool mounted upside down behind the spindle is a good idea. It helps keep the chip flowing out of the groove, and keeps it from getting tangled around the work. You can also mount the tool upside down on your tool post and run the spindle in reverse for parting.

A quick reality check shows that a .156" wide tool will require 2 horsepower at 400 rpm/ .0025" feed. My guess is that if the lathe isn't a geared head, you might not have enough power.

Iscar. They have a molded chip breaker that folds the chip in on itself in a sort of "U" shape while coiling it tightly into a circle. This way the chip doesnt rub or get caught on the side walls of the groove you are cutting. Most of their parting inserts have a helical face which gives the effect of a positive rake. I would go with a .125 wide tool in this case. Feed at .004" per rev. And kick your rpms up a bit.

Don't know, we buy direct from Iscar. Keep an eye on Ebay I suppose, but blades will be self grip type inserts, so be wary of damaged blades.

=================== Try it now.

Picture quality is not as good as I would like, but these are viewable.

Feel free to email with any questions, comments, suggestions, etc.

Unka' George (George McDuffee) .............................. Only in Britain could it be thought a defect to be "too clever by half." The probability is that too many people are too stupid by three-quarters.

John Major (b. 1943), British Conservative politician, prime minister. Quoted in: Observer (London, 7 July 1991).

I could be wrong, but I thought stiffness went up as some power of the thickness, in which case it should be a winning proposition as far as chatter goes. At some point the forces will be too high for my lathe, but going from 0.094" to 0.125" is a small increase in force, and should result in much stiffer cutting tool (I think).

Doug White

Thanks George. Several good ideas there. My bigest problem will be there is no present way to hold anything on the back of the Clausing/Metosa lathe cross slide. It will require some "tricky" mounting. I'll give it some serious consideration ove the next couple of days or weeks. :-) ...lew...

============ On the Clausings we had at the college, you could take one screw loose from a cover on the back of the cross-slide to expose a dovetail. You might check yours.

Unka' George (George McDuffee) .............................. Only in Britain could it be thought a defect to be "too clever by half." The probability is that too many people are too stupid by three-quarters.

John Major (b. 1943), British Conservative politician, prime minister. Quoted in: Observer (London, 7 July 1991).

============ More info:

see following that show rear mounted tool holder

Unka' George (George McDuffee) .............................. Only in Britain could it be thought a defect to be "too clever by half." The probability is that too many people are too stupid by three-quarters.

John Major (b. 1943), British Conservative politician, prime minister. Quoted in: Observer (London, 7 July 1991).

Yep that pix in the second URL looks just like the 8 we have. The rear mounted tool holder is just the ticket. No info on it in our data. Great! Will have to see what we can do about that. Thanks again ...lew...