Back plate metal choice

Hi all

I am about to make a backplate for a 160mm chuck and considering using either EN1a steel or cast iron. I just wondered what thoughts were as to which material is more suitable?

I've seen some use an old dumbbell weight but the mess Cast iron makes when turned down is putting me off so leaning towards the EN1a at the moment.

Thanks Stu

Cast iron finds most favour for backplates because of its supposedly superior vibration damping characteristics and the self lubricating qualities making it less likely to seize up in threaded spindles. Most of the ones I have made are CI, but I did buy a small steel one which has been used as the boss of a faceplate and has caused no trouble at all. The threads are kept clean and lightly oiled. I agree CI is the worst stuff to machine because of the horrible dust, unless you can get some SG cast iron which machines nicely and avoids the mess. If you choose CI, then get a blank of the rough shape, I once made a 160mm out of a cut bar, with twice the mess.

Edited By old mart on 15/02/2021 19:28:25

Chuck back plates are usualymade from SG continuous cast metal. This cast iron resists bending is stable and is less dusty and won't pick up on the spindle. Have a look at M machine metals web site.

David

Edited By David George 1 on 15/02/2021 19:34:48

Plus another one for SG cast iron. For one offs I tend to make a pattern from polystyrene and get a foundry about 25 miles away to cast for me. Not the cheapest approach but you are in control of the amount of machining stock left on.

I have made several back-plates for the Myford out of both cast-iron from an un-machined casting, College Engineering Supplies (I think), and from a 6" noggin of steel, although I don't know what it was it machined pretty freely.

I don't know what lathe you are making the back-plate for or the mounting, but if it's for a Myford/Boxford screw on mounting and this is the lathe it's intended for, I would suggest you obtain an un-machined cast iron casting. The rationale for this suggestion is that, if you haven't got a big lathe to part it off or a big enough power hacksaw/band saw, sawing through a round 6" noggin will take you all day. I have parted 6" in a Colchester with no problem at all but some people seem to have an inordinate amount of trouble with parting off.

When/if you screw-cut the thread, mount the tool up-side down and cut the thread of the rear face of the bore. Doing it this way means you can still use the set-over top-slide method and you don't have to think about reversing the direction of the cross-slide when withdrawing the tool, you can also see what is happening too. If you are making it for a Myford use a nose-threaded tail-stock chuck mounting as a gauge for the thread and be sure to make the register part as accurately a diameter as possible. Put a mark, or better still a positive stop on the lathe bed at just over the length of the thread so you don't accidentally run the tool into the bore. Screw-cutting does not have to be done at the speed of light as the same amount of metal is removed and same number of cuts taken whatever speed the lathe is running at. Cast iron dust is something a vacuum cleaner takes care of in seconds.

Edited By Chris Crew on 15/02/2021 20:15:36

Edited By Chris Crew on 15/02/2021 20:17:39

Thanks everyone, cast it is then. Just as a matter of interest is G250 suitable?

Adan Santander has just made a backing plate for his lathe out of aluminium, athough it is bolt on rather than screwed on. See the thread: "8 inch 4 jaon WM290 lathe".

Do the roughing cuts on the reverse side with an upside down tool like a parting tool

This means 80-90 percent of the mess simply drops down the back

When turning or milling Cast iron, a powerful magnet is placed underneath where the swarf is expected to fall, and then covered with newspaper. Most, not all, sadly, of the swarf does accumulate over the magnet, and by careful manipulation of the paper, afterwards can be dumped in a suitable place.

Howard

Great idea, thanks Howard

You can always put the magnet in to a plastic bag so when you turn the bag inside out the swarf is inside the bag and magnet outside.

David

I was thinking about residual magnetism in something recently and that made me wonder if cast iron was often used for things where residual magnetism would be a problem. I can imagine a steel backplate could be harder to keep clean than cast iron if it retained some magnetism.

Martin C

Having machined a cast iron (probably grey) backplate for my ER32 collet chuck. I'd go for mild steel. The CI dust was right pain to get rid of! Mind you, I like the idea of a magnet, and David's idea of putting it in a plastic bag. I think the large magnets salvaged from speakers would work well.

You still need a vacuum cleaner to catch the graphite.