Lathe backplate problem... or not?

[sploo]

I've got a Colchester Chipmaster (D1-3 spindle nose) and I'm slowly getting myself set up with accessories for work holding, as well as checking the (new to me) lathe over.

The external taper of the spindle nose clocks in at about 5 ten-thou (0.014mm) total indicated runout; as least based on my shonky skills with an indicator. The face of the spindle nose is less than 4 ten-thou (0.01mm). I'm assuming that's OK.

The D1-3 dog plate and 5" chuck on a backplate that came with the lathe, as well as a Pratt 6" chuck on a new D1-3 backplate I bought from Colchester (D1-3 Spindle Nose adaptor for Pratt Burnerd 160mm 3 Jaw Chuck - Colchester Machine Tool Solutions) are perfect in terms of fit, and what-I-understand-to-be acceptable runout.

However, I bought a D1-3 mount ER40 collet chuck and it doesn't sit flat on the spindle nose. It's so far out that I could get a 7 thou feeler gauge in between the back of the chuck plate and the face of the spindle (at one point). Assuming it was just a poorly machined example I sent it back.

I've just taken delivery of a D1-3 backplate from Warco, and it too has a problem. It's more subtle, but I can slip a 1.5 thou (0.038mm) feeler gauge between the rear of the plate and the spindle nose (see the photo below) for maybe 1/6 of the circumference around the spindle. No amount of adjusting D1-3 camlock pins or trying different orientations will fix it.

I tried a bit of engineer's blue on the taper in the backplate and it doesn't seem to be touching the spindle nose taper all the way round.

Given that the spindle nose clocks in well (5 ten-thou runout), and the spindle face appears flat to 4 ten-thou, I assume it must be the adaptor?

 

[chaoticbob]

I had the same problem with a (D1-4) backplate I bought to mount my shop-made ER40 collet chuck. I blued it up, then scratched away with wet'n'dry (backplate obviously!) until I got full contact. I had to remove only a tiny amount of metal to get it sitting tight on the taper and flat on the spindle nose. It ended up tight enough on the taper to need a a knock with a mallet to remove it, and no discernible gap between the plate and the spindle. My reasoning was that even if I screwed up by slightly spoiling the 'perfect' roundness and flatness of the female taper (we're talking tenths), as I was machining the register on the backplate in situ, it would be OK provided I always mounted the backplate in the same orientation. That has proved to be the case.
Bob.

 

[sploo]

I had the same problem with a (D1-4) backplate I bought to mount my shop-made ER40 collet chuck. I blued it up, then scratched away with wet'n'dry (backplate obviously!) until I got full contact. I had to remove only a tiny amount of metal to get it sitting tight on the taper and flat on the spindle nose. It ended up tight enough on the taper to need a a knock with a mallet to remove it, and no discernible gap between the plate and the spindle. My reasoning was that even if I screwed up by slightly spoiling the 'perfect' roundness and flatness of the female taper (we're talking tenths), as I was machining the register on the backplate in situ, it would be OK provided I always mounted the backplate in the same orientation. That has proved to be the case.
Bob.

Thanks Bob. I found a thread on another forum with someone in the same boat, who also lightly.sanded the female.taper. I guess it can't hurt to try.

 

[steve355]

What’s the actual runout at the collet?
is everything absolutely clean?
are there any burrs etc that can easily be taken off?

 

[sploo]

What’s the actual runout at the collet?
is everything absolutely clean?
are there any burrs etc that can easily be taken off?

The collet chuck I returned? Massive. With a 7 thou gap at one point between the collect chuck backplate and spindle face it was unusable.

Clean - yep. Burrs - no.

There wasn't any obvious (visible) defects on the collect chuck backplate, or this new Warco backplate. Seems that maybe the Chinese made D1-3 backplates may generally have their female tapers ground a bit undersized (at least, based on a sample of 2 I've seen so far).

 

[sploo]

Got the backplate fixed.

I set the compound slide on the lathe to match the angle of the D1-3 taper on the spindle using a dial gauge, then cut a chunk of aluminium such that the smallest diameter was a bit smaller than the spindle nose taper:

The backplate (with studs removed) appeared to be a decent fit onto this taper; indicating the compound angle was acceptably accurate:

I then removed the chuck and sat it face up. With some valve grinding paste on the aluminium taper I dropped the faceplate onto the taper and carefully started to grind the faceplate taper. After a few rounds of grinding and test fitting the aluminium taper looked like this:

End result is that the faceplate now sits well on the spindle with no gaps (at least, nothing I can get a feeler gauge into). Once the camlocks are released, removing the faceplate requires a gentle tap with a rubber faced hammer. A quick check on the sides and front of the (not yet machined) faceplate shows about 3 ten-thou of runout. I'll take that.