Working a piece of rough stock

[fluxcored]

Hi All

Within the next week or two I'll be attempting to turn a gear blank out of a cast aluminum piece of round stock. The problem is the stock's diameter is not uniform and the ends are'nt totally true. I think it's safe to say that at any point over the length of the stock a variation of 2-3 mm is possible.

I also will need to centre drill however have an immediate problem with that because the ends are'nt exactly the same diameter and is not totally round either.

It's also so big that I think that I''l have to turn it between centres otherwise it'll be close fit in my 3 jaw chuck using the outside jaws.

Low tech solutions are preferred. I have'nt got a milling machine or a bandsaw - hopefully that'll be remedied in the next year or two.

Any help will be appreciated.

Regards.

[Darren]

What size is it and how big is your lathe?

[John Hill]

Hi
I think the best thing is to choose a 'centre' as best you can by eye or with a rule, mark the centre with a dot punch and do the same on the other end.

Then mount the work between centres so that you can turn the piece, by hand, and judge if your centres are wide of the mark, mark new centres and repeat if necessary.  You can move a dot punch dimple a little by using the punch at an angle.

It is not mandatory to centre drill in the lathe so you can use a drill press or even a hand drill as available.  Once the centres are drilled you can remount it in the lathe and turn it true in no time at all.

If the work piece is short (more like a disc than a bar) you could mark one centre then drill through with your smallest drill to line up a centre on the other side.

Maybe you do not have a lathe dog big enough to drive it?  You can wrap a strong cord around the work and anchor it to the lathe chuck but be careful of loose ends and the possibility of anything getting entangled.  If your final work will have any holes in it, other than a centre hole, you could drill a hole in that position and thread the cord through or even put a bolt in the hole.

An alternative to all above would be to drill a hole through the approximate centre and mount the work on a mandrel though this would really only be practical on a short piece.

I have only a few months experience in this hobby so perhaps others will have better ideas.

cheers
John

[fluxcored]

Gee, thanx for the quick reply Darren. Where would I be without the internet!

OK, my lathe is an old Boxford CSB. I've only got a 100mm 3 jaw chuck. The bar will be roughly 50mm thick but as mention will vary across it's length. I'll need to turn that down to 48 or 46mm - did a rough measurement last night. The length of the bar will not exceed 100mm but I mean I only need a fraction of that so I can cut it down with a hacksaw to a little bit more than the thickness of the gear that I need.

I remember when I made a hammer - that really was a howto on not making a hammer - that I had trouble with a 50mm piece of BMS. It chucked into the 3 jaw using the outside jaws but I had to take very light cuts. Same will happen here but I guess it'll go better since it's aluminum.

[Darren]

Are we talking 50mm diameter and 100mm long?

If you have a four jaw chuck center it the best you can in that and do as John says and center the other end as best you can by measuring. Hold other end with a rotating center.

You can then turn it true taking light cuts at first, and with ally it should be an easy task.

I hope I understood you right?

[fluxcored]

John, Darren good tips!!

Darren, yes but I can be flexible to the length of the piece I'm going to chuck - I only need to be able to make a gear from that. I was stupid in thinking it's best to chuck the whole bar and true that up then cut a section off for the gear.

I think I'll make the length as short as possible (gear thickness + a bit extra) and drill from the one side right through and mount on a mandrel. That'll work.. 

Guys, thanx a lot!!