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jsn_joiner
01-08-2007, 09:17 AM
in the build a cutoff attachment for your lathe it says do not try this stunt with a threaded chuck, as the chuck may walk off the machine. My question is Bob is using a SB9" as well as i am and what other chuck is there they all screw on the nose? I am interested in making this but if i cant use it with the chucks i have it is not worth my time.

JCHannum
01-08-2007, 10:08 AM
The article details building a rear mounted cutoff toolholder. This permits cutting off with an inverted tool with the lathe running in the forward direction.

Many older lathes have threaded chucks that will unscrew if run in reverse. There are several other chuck mounting systems that key or directly attach the chuck to the spindle to prevent this from occurring.

Swarf&Sparks
01-08-2007, 10:17 AM
Am I missing something here? A rear parting tool is used upside down. The lathe runs in its normal direction.
Likewise, I always run boring bars upside-down at the back of the bore.

JCHannum
01-08-2007, 10:37 AM
The introduction to the article describes using an inverted toolholder in the normal position, using a taperlock chuck. It goes on to state that this cannot be done on a threaded mount and details the construction of a rearmounted tool post.

Swarf&Sparks
01-08-2007, 10:49 AM
OK, thanks JC. Got the picture now.
Threaded chuck could get very untidy run backwards :(

jsn_joiner
01-08-2007, 12:21 PM
ok if i get this straight you can use this tool being made because you still run the lathe in the right direction because you mount the tool upside down? if it was on the correct side you would have to run the lathe backwards which would unscrew the chuck?

JCHannum
01-08-2007, 12:30 PM
You've got it.

Mike W
01-08-2007, 12:48 PM
I made this rear mounted tool post that uses a KDK parting tool holder. It works great.

http://img.photobucket.com/albums/v110/tek798/Lathe/Reartoolholder.jpg

pcarpenter
01-08-2007, 03:44 PM
I posted this with regard to another pic of a QC toolpost mounted rear cutoff tool holder once before.

I think it is probably pretty questionable to make one of that sort from a safety perspective if the spindle is to be run forward while cutting (blade mounted inverted). With a typical Aloris style tool holder used properly, the cutting forces are pushing the holder into place, down, and against a stop nut. Used in reverse, the forces are attempting to lift the whole tool holder and hurl it at the operator.

In most of these QC tool posts, the piston or wedge that is used to hold the individual tool holder from movement does not have to hold it against cutting forces. The stop nut can bear the load while the piston merely prevents movement. Additionally, a standard cutoff blade holder should have some taper to the "seat" that holds the tapered or t-shaped blade. Put the blade in upside down and the blade is no longer square to the work, making it more likely to be grabbed in the slot that is formed as you are parting.

A fixed rear-mounted cutoff tool holder does not have this same risk of being picked up and hurled at the operator.

jsn_joiner
01-08-2007, 04:15 PM
Thanks for all the replies im going to make one right now all i ahve is the crap one that came with my lathe and the blade tends to be pushed back instead of cutting and lots of chatter.

jason

BillH
01-08-2007, 04:19 PM
Besides the chuck unscrewing on a SB type lathe, you also run the risk of lifting the slide off the table, the force is no longer being forced down to the ways, just the opposite.

J Tiers
01-08-2007, 05:30 PM
You folks got your MW already?

I JUST GOT my copy of HSM for Jan/Feb, the one with the rotary table article.

Being as how I live nearly in the middle of the US, this seems odd.....

But I guess that since HSM and MW have to be shipped from the printing plant in Belarus, I suppose that isn't too bad..... :rolleyes:

I could drive from here to VP HQ in one day...... OY...

JCHannum
01-08-2007, 05:55 PM
You folks got your MW already?

I JUST GOT my copy of HSM for Jan/Feb, the one with the rotary table article.

Being as how I live nearly in the middle of the US, this seems odd.....

But I guess that since HSM and MW have to be shipped from the printing plant in Belarus, I suppose that isn't too bad..... :rolleyes:

I could drive from here to VP HQ in one day...... OY...

Relax Jerry, the Machinist's Workshop issue being discussed is Dec/Jan.

jdunmyer
01-08-2007, 07:50 PM
Jason,
My first lathe was a 1933 Atlas and part of the included tooling was a parting tool. It was very frustrating and I ended up using a hacksaw for almost all cutoff work. Since then, I've learned a few things:

A lantern-type toolpost isn't very rigid, most of my problems have been solved with later lathes that use a quick-change (Aloris, or similar) toolpost. Using a narrower blade helps: the Atlas had a 1/8" wide blade, the one for my H.F. 7X10 uses a 1/16" blade. Checking the sharpness with a magnifier glass and getting the thing sharp really helps. It's best to sharpen on a machine that has an adjustable toolrest, even a 1" belt grinder will work well. The point of the tool must be exactly on center. And use some sort of cutting fluid, Tap Magic is what I use mostly, but pipe-threading oil is good also. Run the speed at about 2/3 what you'd use for turning.

J Tiers
01-08-2007, 09:27 PM
Relax Jerry, the Machinist's Workshop issue being discussed is Dec/Jan.

WEll, I'm not at all sure I got THAT one......!

I hadn't got a magazine for quite a while prior to this HSM....... and I get both of them.

Must be time to look behind the boots and umbrellas, the mailbox is inside the coat closet...... perhaps it slid down. :D

TECHSHOP
01-09-2007, 02:47 AM
J Tiers:

Didn't you get the memo?

There is no Federal Budget for FY07, so only your bills will be delivered by the US Mail!