Chuck backplate material choice

Cast iron is what most OE parts would be made from. It's tough, durable, damps vibrations reasonable well and is very easy to machine. It machines dry, swarf comes off very cleanly as dust or fine chips and it's nice to drill and tap. Steel would be second choice but ordinary mild steel won't machine as cleanly as cast iron and you'll end up with a rats nest of stringy swarf everywhere. Leaded mild cuts pretty nicely though. I'd avoid aluminium for something like this. It's as strong as cast iron and easy to machine but soft and easily damaged. You want something that registers very positively.

-- Dave Baker Puma Race Engines

Thanks Dave, cast iron it is then!

Cheers, Rob

A good source for this is cast iron dumb-bell weight discs - I made a face plate a couple of years ago from one - 2 kg is about 6in diameter, and will cost about 4 quid from a sports shop I pay about 50p/kg at the car boot for them

Often wondered if they were suitable for machining - was there a hard skin or did they machine nicely?

AWEM

Unpredictable. I machined a disk and it was so nice to machine. Then a rectangular weight that was a real pain. And I scraped a touching prism out of it. :-(

Nick

very nicely, no voids or anything - dunno if that can be said for every single disk from every manufacturer of course.

Very interesting, I just happen to have some 5kg weights (nearly 8" dia) lying around that aren't being used for anything worthwhile, think I'll chuck one up and see what I can get out of it!! Thanks for the tip!

Cheers, Rob

Bluddy 'ell!!

Just spent the last couple of hours convincing that lump of pig iron lathe to cut that lump of pig iron weight. I've discovered the joys of the hard skin phenomenon in cast iron, which was made even more enjoyable by the raised lettering cast on the weight. Still I've managed to get one side faced off pretty well despite not being able to find a decent compromise speed, not surprising when cutting from 1" to

Cheers, Rob

You are allowed to change speed as you go, and it is usual to face inwards, from 7" to 1".

Its boring otherwise.

Regards, Tony

I was taught at school to face outwards, and where some lathes are set up so that facing inwards goes with the same settings as turning towards the chuck, with others the opposite is true. I wonder wheter there's some sort of local or national 'tradition', which varies from place to place?

Cheers Tim

Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service

I picked up facing from the middle out from one of the workshop series books, I seem to remember it saying that it gave a better finish, but with this job I have been cutting in both directions anyway just to get through the damn stuff. As for changing speeds half way, well I could do but that would increase the job time tenfold as I'd be battling with a crappy pulley system every 30s. To be honest the 400rpm I ended up on did an OK job, it was only on the last outer inch that the lathe struggled.

Not had a chance to get back on it though due to lower back pain and sciatica making standing at the lathe a bit of an issue. Great isn't it, I'm 34 and falling apart!!

Cheers, Rob

If I want to remove lots of material, I face inwards. For a nice cut, I face outwards.

Nick

That's what happens when you go around lifting weights...

Another technique to use when trying to remove as much as possible is to set the speed for the outside and rough face to part way towards the centre until you've removed nearly as much width as you need. Then set the speed higher and do the inside half. Then do a finishing cut over the whole diameter.

Mark Rand RTFM

Haha, that stopped about 4 weeks after I bought the weights, about 15 years ago ;)

That makes sense. I'm actually tempted to bung it on the mill, now that I've got the one side faced, to hack off the excess on the other side, no issues with varying cutter speed at least - and it would be a good test of the mill now that it's pretty much ready for action.

Cheers, Rob

Cheaper on the lathe with HSS-bits that you can regrind by hand than dulling your valuable milling bits. IMHO

Nick

I usually rough facing forward cutting with the tip of the tool. Then finish backing out, cutting with the side which is a cutting edge but has been angled to give a shallow back clearance angle.

By backing out this way the material gets engaged (cut) progressively. In the middle of the cut, the face looks like it has a thin obtuse frustum between two cylindrical bodies the frustum is as high as the depth of cut and the two diameter are in the order of 2-3 mm depending on the clearance angle given when facing forward.

This description is not literally accurate but should make sense to those familiar with facing on a lathe.

Mauro

At what speed ?

As an update, I ploughed though the other side yesterday on the lathe, so it's just ready for drilling now. Alas we had a power cut today from just after noon to just before 7pm, so no drilling in other words. Life without power is soooooooooo boring!!

Now why did it seem like I cleaned up much more iron dust off my lathe at the end of the day than I could possibly have removed? I started with a 5kg weight, there's still at least 1kg of it left, yet I seem to have scraped up about 10kg of dust ;-)

Now I just need to figure the best way to centre my newly acquired rotary table under the mill spindle and I'll be set! Got a feeling it involves holding a DTI in a chuck and turning that against the bore in the table, that sounds resonable to me anyway.

Cheers, Rob