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ZINOM
10-19-2003, 09:47 AM
I was thinking of making a cut-off tool holder, and after looking at them in catalogs and magazines I see some hold the blade mounted at an angle and some hold it straight......it'd be easier for me to make it straight....is that acceptable?

Also, am I looking to buy flat blades, or the "T" shaped?

I work with 1018 and brass for the most part.

Thanks all,

John

wierdscience
10-19-2003, 12:46 PM
HSS cutoff blades are good for two things,wood and plastic.

Do yourself a favor and get yourself an insert cutoff blade,their cheap on ebay last one I bought I gave $12.00 including shipping.

The straight type holders are the easist to use,if you really want to get a hss blade get cobalt and whatever you do no matter how much you are tempted don't grind a chipbreaker in the top of the blade,this makes for hours of frustration.

spope14
10-19-2003, 01:23 PM
P type blades (t shaped). Colbalt blades - 5% is what I use. more is probably better. I prefer the angled type of holders as they are a bit more forgiving. I have three angled type and two straight type in the shop.

The first trick to both is making absolutely sure the blade in indicated exactly perpendicular to the C/L of the machine, or with your crossfeed travel. I usually seek .0001 for the entire cutoff length, but hey, I am picky. Before you start enything though, take the the blade OUT of the holder, clean out the holder and blade seat and blade, put the blade about 1/8" beyond the length of desired cut (eliminate overhang), seat properly and chack it all out. An improperly seated or oiled up seat is fatal to the blade eventually (BaNG Snap)

The second trick is centering. Small stuff right on center (1" or less), bigger stuff slightly above center (flex).

Third trick, I am very conservative on speed and feed. Low speed. usually about 100 RPM, and feed at minimum. Use the power feed. Took me years to get that confidence as I truly hate cutoff to the deghree I absolutely love threading and knurling. The power feed prevents(prevents, but not eliminates) chatter and eventual grab. If chatter develops, kick up the feed one notch at a time.

Fourth trick - LUBE. Many say not to lube brass or Cast- do it with the cutoffs. I had a whole pile of busted blades before, only go through one a year now, and i use these materials commonly.

Fifth trick - cleaning out the chips. The little rollers that are so cool.....get them OUTTA THERE. Blow them out, brush them out (stopped machine), whatever.

Sixth trick - before anything starts, grind a 15 to 25 degree angle on the blade, the tip to the cutoff part end. relieves the "plowing" effect of a straight blade, and gives a "lead point" in cutting off.

I use my HSS blades for everything from wood to delrin to H13 and D2 tool steel. They work OK (harder stuff is a pain in the fanny, but they work).

Carbide blades are good, I have a couple of them. Problems occur when you do not center, indicate to the cut, or overspeed and feed - or when "grab" occurs. I have four more indexible tools in the shop with blown out ends because of the "overconfidence" the students get using them.

I would look into a carbide insert tool for the harder stuff, they cost a bit. HSS also has a place, but after the cost of blade and holder (holders at about $70.00 for aloris, about 36 for Yuasa), and blades at 15 each, you might be served to look into the insert type, though costs equal out after the first insert.

I prefer HSS myself though, more forgiving cutting material.


[This message has been edited by spope14 (edited 10-19-2003).]

Ian B
10-19-2003, 02:16 PM
Biggest favour I ever did myself when parting off with a small lathe was to make a rear toolpost and mount the tool upside-down.

The chips fall out easily, you can dribble lube oil down onto the tool, and I get far less jamups (followed by a loud bang) this way. Note far less - not none!

Ian

beckley23
10-19-2003, 04:41 PM
ZINOM, You don't say what size lathe you have, but from my experience rigidity of set-up and the machine is paramount. The closer to the spindle the better. I gave up using HSS cut-off blades years ago and switched to the inserted type because chip formation and clearing is so much better with the inserts. In my situation I can't be stopping the machine to clear chips very often, and cutting off with HSS and chip clearing was causing a lot of problems.
The above being said, get the tool square to the centerline. I like my cut-off a few thou,3-5, over center, and I run the machine as fast as possible on the rear cut off position, as the conditions permit, and I slow it down for the front. Feed is about .0025/rev under power and about the same hand feeding. I also use flood coolant.
The largest piece I remember cutting off was 2-1/2 OD X 1-1/2" ID 304 SS at 734 RPM .0025" feed on my #5 J&L.
Just remember rigidity of the machine and set up is very important.
Harry

chkz
10-19-2003, 07:55 PM
was gonna ask for a few tips on parting-off myself....thanks guys. Just bought a cheap parting blade holder and some polish blades (5/8 x 3/32)...."Groz" brand I think. Got tired of grinding & grinding a perfectly good piece of tool stock only to make a half-assed parting tool! I've already broken one of the rules I see by grinding a "chip breaker" on the top...and you're certainly right...that is NOT the way to go...I'll try to slow it down as well...was parting a piece of crs about 2-1/2 the other day...got about half way through and things just got wayyyy too damn "hot & bothered"...(I was going for the fast rev/slow feed option there)...ended up finishing that one with a hacksaw...didn't want to waste what was left of my now somewhat "blue-ish" blade!!! Funny...I was waiting for the "snap"...but it never came...really hogged in at one point too...anyhow...practice makes perfect (or close-enough) right???

take care,
chris

beckley23
10-19-2003, 10:48 PM
I started in this business as a hobbiest. I have owned and used many different makes and sizes of lathes from Watchmakers to Monarchs. When I first started, parting off, as some if not all have found out, was a nightmare. When I got my 13" Sheldon, in 1983, I also bought an Aloris style toolpost. It was the difference between night and day in parting off. Not only was the Sheldon with its generous spindle bearings much more rigid and massive than my previous lathes but the rigidity of the toolpost added greatly to rigidity of the cut off tool.It also helped that the Sheldon had just been reconditioned.
My observations since have led me to conclude that one should pay very close attention to the condition of the machine tool itself. A lathe with a lot of wear in the cross slide and carriage does not make a very good platform for cutting off. Do not make the assumption that your cut off tool is the problem, even if your lathe is new. Check it out, you may be surprised by what you find. I have also observed that the heavier the lathe the easier cutting off is. I have no problems cutting off in my #3W&S(3500 lbs), #5 J&L(6000 lbs), 16" Monarch (5400 lbs) and it doesn't make any difference whether power or hand feeding and I do run them as fast as the job permits, in fact I can't remember running under 500 RPM, it is often at 1480 RPM on the W&S up to 1-1/2" dia. The only time I have trouble is when the insert is getting dull or has a chip in the edge. Observation of the chip form is an excellent indicator, as is the finish of the faces.
Harry