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View Full Version : Positive or Negative rake?????



G.A. Ewen
12-08-2003, 03:48 PM
I am trying to cut new teeth in the gears off an old South Bend headstock using my shaper. The problem is that the gears were brought to me already welded. The weld metal is some kind of specialty brazing rod that was pasted out by a salesman (I really dislike those guys) and of course there is no technical data with it. With the shaper tool ground by the book it skids along the surface of the weld or it digs in and pushes the dividing head of the shaper table, depending on how much feed you give it. http://bbs.homeshopmachinist.net//mad.gif

Should I grind a more positive rake or try a negative rake?

This weld metal does not file very well either

Any help is greatly appreciated.

JCHannum
12-08-2003, 03:57 PM
It sounds like it might be a hard surfacing rod. If you can't cut it with a file, it will be hard to machine. Maybe a carbide cutter, or grind it off and start over by brazing?
I always preferred to replace teeth by brazing. If strength is a concern, drill & tap & install a short steel stub where tooth is missing and build up braze around that.

G.A. Ewen
12-08-2003, 07:01 PM
JC,
I would describe the weld metal as "slippery" rather than hard. A file will cut it but the cuttings are as fine as dust.

wierdscience
12-08-2003, 10:54 PM
Do you mean SB headstock gears as in cast iron ones?If so and they have been welded chances are the weld sucked up a bunch of carbon from the cast,in that case either grind or annel the crap out of them.

Evan
12-09-2003, 03:59 AM
George,

What color is the "weld" metal?

jlrsn
12-09-2003, 05:27 AM
Are you talking about the cast iron gear that is part of the Step Pulley Assembly or the forward Bull Gear? I've machined the broken cast iron gear off of the Step Pulley Assembly a few times in the past and replaced it with a steel Boston Gear that I machined for a press fit. Those gears have lasted over 20 years the last I've checked and run quiet.

G.A. Ewen
12-09-2003, 10:28 AM
Both of the 66 tooth gears have teeth missing. I suspect that someone got over enthusiastic when trying to remove a stuck chuck. The spindle shaft still had the chuck back plate on it when it was brought to me. The first thing that I did was take it off (thirty seconds work when you know how) and it was clear that it had not been off for some time.

The weld metal is a 'silver brass' color.

JCHannum
12-09-2003, 10:58 AM
The weld, for some reason is hard, well duh. Annealing as suggested may work, or carbide cutter. I doubt changing the rake will help.
You may be able to grind some of the weld off, and get to a machineable area if it is a surface condition.
I would not fool with it for too long, mystery weld is like mystery metal. If you do manage to finally chew some teeth out, how do you know the remainder will not break away from the parent metal. Easiest solution might be to grind it off and repair with known, successful methods.

Pete Burne
12-09-2003, 07:13 PM
G.A.

What is your secret for removing a stuck threaded chuck flange.

I have one stuck on my 12" x 5' Hendey and I want to get it free so I can switch between my 8' 3 jaw and my 10" 4 jaw. I haven't forced the issue because I don't want to break gear teeth. HELP!!!

Thanks,

Pete

G.A. Ewen
12-09-2003, 07:51 PM
Pete,
You've heard the shop saying "Don't get mad, Get a bigger hammer"? WRONG
Don't get mad, get a faster hammer.

I used a piece of square bar 1 x 1 x 18" that has a dimple drilled at about 6" from one end. Lock up the spindle, tighten the chuck jaws on the undrilled end of the bar, push down on the drilled end while using an air chisel with a blunt round nosed bit in the dimple.

Works for me. Let us know how you make out.

Evan
12-09-2003, 08:47 PM
Pete,

You might try the technique recommended by South Bend. Put the lathe in lowest back gear and use a stick between a jaw and the rear way. Jog motor in reverse. That's how I take my chucks off. I use a 1"x1"x6" lead bar instead of a stick.

Thrud
12-10-2003, 03:29 AM
George

Try a negative rake carbide insert if you have them and take it slow. I use these to modify hardened & ground MT shanks all the time.

I use a Ridgid Strap wrench (cotton strap) on my chucks - no one is cranking on my jaws! These strap wrenches rule - they never mar the surfaces - handy for tight assemblies too.