Chuck backplate from steel weldment?

The $45 price for a cast iron chuck backplate to my door has me wondering if I would be fine welding up a couple pieces of 1/4" scrap mild steel and then stress relieving it in the oven for an hour or so. This will be for mounting my 3" mini-lathe chuck to my 4" rotary table. Any reason not to do this?

Mike

Mike

Why not cut a 4" diameter piece and drill to suit fixing to the chuck with c/s head screws and then drill to screw to the table tee slots using longer than normal tee nut pieces.

You can use separate pieces for locating the chuck register and to provide an arbor to locate the table centre.

Emgee

Edited By Emgee on 15/03/2022 20:59:49

spelling corrections

Edited By Emgee on 15/03/2022 21:01:39

Hi Emgee,

I assumed that 1/4" steel wasn't thick enough, given that the cast iron back plate for sale is 5/8" thick with another 1/8" for the chuck register.

Mike

Hi Mike

You will be screwing the plate to the chuck and all will be as one unit as the table,plate and chuck all make contact, If it didn't work out to be rigid enough you can always double up the plate.

Emgee

Backplate only needed to adapt chuck fitting to table, it will add hardly any rigidity and just eat daylight. For my 6" RT I have drilled and tapped 4 M10 holes in the table top, so I can remove my 4J chuck from its backplate and bolt to the table. So, you adapt your 3J to fit so you have the basic runout in the chuck plus any inaccuracy in the adapter, the work doesn't run true, what do you do then? A 4 jaw is easier to fit and you can adjust for concentricity.

Hi MikeK, nothing wrong with welding steel plate, but you will be wasting money trying to stress relive it in your oven, assuming you are talking about a domestic oven, as it won't get hot enough. Stress relieving steel starts at around 600 C.

Regards Nick.

Thanks, guys!

So, if I make this out of steel...don't bother stress relieving it? I just thought the welding would do a number on it. I do have some thick plates of aluminum, plenty big enough...though the registration boss will probably take a beating with mounting and dismounting. Maybe I should just spend the $45.

Mike

Just use a steel billet. Maybe a weight from a weight lifting set if the note is small is small enough.

This seller on eBay does an 80 mm a 40 mm billet for £9 with £6 postage.
(Search his other listings.) He may be able to cut the size you need,

Other sellers are available.

I found a 4" x 1/2" steel disc on eBay for under $8US. That should do the trick. A36 steel shouldn't need any stress relieving so that's good. It would be nice if I could fit my 4-jaw on my rotary table, but both are 4" so that's out.

Mike

Hi Mike,

I have done the same as you want to do, mount a 3-jaw SC chuck on my Rotary Table. I used a 10mm thick plate of mild steel. I drilled 4 holes so it could bemounted on my RT, first I drilled tapping size holes and tapped them. Then I could mount the workpiece on the lathe faceplate and face each side and turn the spigot for the chuck. I have used this chuck for over a decade. Good luck.

Thor

Couple of things going on here:

1. Mild-steel versus Cast-iron. In theory cast-iron is better for this application because it absorbs vibration, whereas steel 'rings'.
2. There's a risk welding will deform a plate made by joining bits mild-steel together, especially if the welder is semi-skilled. Distortion is hard to correct if it happens.

In practice, I doubt the difference between dead cast-iron and ringing steel matters much on a Rotary Table.

Making the plate from a lump of metal big enough in the first place rather than welding avoids the risk and the cost of fixing it if it goes wrong. If welding goes well, Mike will save money. If it goes very badly, a waste of time and money. Mild distortion might not be difficult to fix, so another win. The method is unreliable.

Problem with a heat-warped precision item is how to fix it. A domestic oven isn't hot enough because relief soaking requires higher temperatures for several hours. Heating with a torch requires judgement. The warped item could be machined to shape, but it might move again due to stress relief. Certainly not impossible, but more unpredictable than I care for.

Have to confess I'm partly negative because I don't enjoy this type of problem solving and would rather buy my way out of trouble by paying for a suitable cast-iron or mild-steel disc. Others would relish the challenge and delight in the experience. I don't think there's a straightforward answer. It comes down to what Mike has to hand and his appetite for adventure. Be good to know how it works out, dazzling triumph, miserable failure, or 'good enough'!

Dave

Ketan at ARC spent some time on the phone to me, talking about cast iron versus steel for back plate use. He maintained that steel was just fine in this application and he knows the business.

Andrew.

MikeK:

I would encourage you to try the weldment approach. Here is one I made to rescue a condemned hobby drill press:

Rough turning the disc and tube allows easy vee joint preparation and after welding the result is re-machined (mine hasn't quite cleaned up).

I fabricated my Versatile Dividing Head body from steel welded together. Stress relieved it by heating up to a dull red with a 1" propane torch and some fire bricks then buried it in a bucket of lime to cool slowly.

But for your chuck mount on rotary table, your bit of unwelded flat steel plate should work ok as is.

Cast iron has the other advantage of being more resistant to deformation than steel under compression. But the main reason it is used for things like chuck backplates I think is mostly cost. Cast iron for odd shapes is the cheapest way to go.

I want to put a new Sanou or similar chuck on my old Myford, which will require a backing plate, which I can not buy in Australia. With the current UK import shipping delay to Australia being two months due to Covid backlog at customs, I will be welding two discs of steel together, stress relieving as above, and machining it to fit. As Ketan has told others above, it should be just fine. Many of the chuck bodies themselves these days are steel and seem to also be just fine.

Thanks for your experience, Thor...I endeavor to match it.

Thanks, Dave. Experience is a good teacher...Would have liked to do this with welding, as I wouldn't need to buy anything, but I'm going to give it a go with an eBay lump. Vendor says the disc is plasma cut under water so it should be ready for my machinations.

Hi Andrew,

Ketan’s backplates are fine, I have used them before and am about to order 2 more if the price is still reasonable.

Not ordered anything model engineering related from anybody for 8 years

Thanks, Andrew, ega, and Hopper.