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View Full Version : Aluminum backplate for chuck?



brunneng
11-24-2002, 07:42 PM
A while back to got some advise here on making a cast iron backplate for a bison collet chuck. I've been working on making ne from a piece 1" cast iron but my small lathe just doesn't seem to have enough mass to hold everything rigid enough to get a smooth finish. I've been setting my speeds according to The Handbook.

Can aluminum be used for an effective backplate in this case? Since all work will be held in collets, the largest dia that will worked is a 1-1/16". So I'm thinking that a 1" thick piece of aluminum will work and I know I can get a smooth cut on that.

Thanks
Kevin

Dick Payne
11-24-2002, 08:28 PM
I am a beginner but I would not trust aluminum for threaded holes to hold even a collet chuck. If you bolt all the way through and use a steel nut and bolt I think it would be OK. I make 1" thick aluminum face plate fixtures for mounting of small jobs that I want to use over and over.
You don't need a great finish on a back plate in my opinion.
How rough are you talking about?
Kevin:
I use a chineese brazed C2 carbide tool bit on a Smithy 1220 3in1 lathe and get good results. I do not extend the tool bit very far from the tool holder. I usually run it slow to get maximum torque for back plates.
I take small cuts and it takes a long time to cut a large plate down to size.

What kind and size of lathe do you have that won't give you a good finish on cast iron?

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Dick

docsteve66
11-24-2002, 08:52 PM
brunneng: you probaly know this already, but cast iron has a "coating". You will have to get that thick skin cut away. the coating material is abrasive. after you get underthe scale (coating) I 'd try a HSS tool. I like to work cast iron (the good stuff, intended to be worked).
Steve

Thrud
11-24-2002, 10:30 PM
Kevin
Is the spindle threaded? If so, you can buy a semi-finished backplate and just fit it to the chuck (Bison has beauties - void free, no crusties). If you are using brazed carbide tools that is your problem. Dig out some HSS and you will not have a problem. If you are using inserts, make sure they are positive rake, as this requires the least horsepower and is easier on the lathe.

Brazed carbide comes with what I would call an unfinished edge. I always sharpen (side only on lathe bits - not the top!) and then hone them with a 400x CBN or 600x Diamond file.

You can also hone your wood router bits to cut better, but only hone the top - not the profile of the router bits! This is because when they are ground they only grind the top or the carbide to retain their orginial profile. Touching them up greatly improves how they cut.

brunneng
11-25-2002, 03:25 PM
The lathe is a Grizzly 7x12 mini-lathe. The chucks bolt on with an alignment recess.

I wasn't having trouble getting a good cut on the circumference. I had to use a carbide boring bar to get back far enough to turn the edge.
I ran into problems making the facing cuts which were into the sawn surface. I'm getting lots of chatter on the surface. I've tried HSS and carbide bits. It just vibrates the whole lathe. I think it's just not heavy/stiff enough. The carbide bits are indexable so they aren't the brazed type.

I wanted to use the collet chuck because I'm converting the lathe to light cnc work. I realize it might just be too big for the lathe. I'm working on plans to make a new spindle that will accept 5C collets in place of MT#3.

If I could afford a bigger lathe right now I'd do all the work on it and try a final finishing cut on this lathe.

Thanks

Dick Payne
11-25-2002, 05:01 PM
Doc and Thrud:
I am currious about the use of aluminum. Was I being too cautious on my previous response?

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Dick

kap pullen
11-25-2002, 05:34 PM
Brunneng,

Sure aluminum should work.
Keep it on the heavy side.
You only have a light duty lathe.
If the holes wear out five years from now,
put helicoils in them. If the spindle hole wears, loctite in a threaded bush.
By then you'll have a heave duty job (lathe) anywayright?

Don't worry, be happy!

kap

brunneng
11-25-2002, 07:48 PM
Yeah, if the disk worked for a year I'd be happy. It's just going to be light duty cutting al, brass and some steel under cnc control so it'll be nice steady feeds.

Though, so far, I do think that the headstock is big enough to machine a new spindle for 5C collets, but I'm still working on that design. It would definately be more accurate than what comes out of the Seig factory for this size machine. I could also fit it with real tapered-roller bearings.

Thrud
11-25-2002, 11:09 PM
Kevin
It might be easier to just start the lathe you want from scratch than to do a 5C spindle for the little lathe. You would need at least 2" diameter spindle and tapered bearing would bring that out to about 4" for the headstock - that is a lot of meat!

Perhaps a Gingery approach to the problem?

docsteve66
11-26-2002, 12:46 PM
First on the use of Al. Kap says (better) what I would say, if i had said it!.

Kevin: when that thing starts to chatter, put your fingers alongside the ways, dove tails, gibs, compound. If the chatter is there then some ting is loose some where. You shold be able to cut cast iron or aluminum whith no chatter if the tool hieght is rite, every thing is tight. TEll you the miserable truth, many yers ago (50 or so) I could not make a good new lathe cut with out chattering. A tweak here, a hammer there and it finaly started working ok. I have no idea waht I really did. Funny things was I could make chatter on ANY lathe. Getting rid of the cahtter was the problem http://bbs.homeshopmachinist.net//smile.gif. Few years ago, I wanted to show some kids who were having chatter problems and I had real trouble MAKING it chatter. Its the innnate preversity of inanimate objects!!!. Once you learn how to set things up, rite, tite, speeds feeds etc I bet you will wonder how you ever made the damn thing embarass you. Keep trying. Your lathe, even if worn out will do Al or cast just fine. Its you not the lathe I bet a beer. http://bbs.homeshopmachinist.net//smile.gif
Steve
(edit comment- when you feel for the loose stuff, dont forget to feel way down on the legs and to the floor- light lath on three legs will squirm like..... naw you guys got dirty minds-)

[This message has been edited by docsteve66 (edited 11-26-2002).]