Lathe spindle alignment

[Iain DownsParticipant @iaindowns78295]

Huub – not using a top slid and I suspect my boring bar is the same as yours.

Which makes me ask a question. Previously I've drilled out to 14mm with a blacksmith drill, but not been happy with the finish or accuracy. I'm asking myself if I stopped at 12mm this time with a 'good' drill. Perhaps that's the root issue. I will put a 14mm hole in and see if that makes things better. I don't think I saw any rubbing (and I think I checked), but don't trust my memory).

That will be embarrassing if that's the case!

Iain

[HuubParticipant @huub]

From roughing (drilling) to finishing (turning) it takes 3 passes at an equal cutting depth if the setup (not a rigid lathe, large tool stick out, large thin stock stick out) is not rigid. Getting a decent finish under these conditions is always a challenge. You have to reduce the cutting forces to succeed. Reducing the feed/rev, depth of cut and to some degree, the RPM is the only thing you can do.
The insert is also important if you can't run under the conditions advised by the manufacturer. In general, I use finishing inserts on my not rigid desktop lathes. Large (DCMT11xxxx, WNMG08xxxx, etc) inserts are generally made for heavy turning conditions. Small inserts perform better under light cutting conditions.
I have 3 boxes of TCMT110204 VT15TF of the same brand and supplier and 3 boxes of other brands and suppliers. One of the 3 boxes gives an outstanding finish, a lot better than the other 2 boxes and the best of all 6 boxes of this insert type I have. So I use this box only for making gear gutters. All my inserts are from web shops and even the branded are probably counter fait. Never the less, 8 of 10 boxes perform well for my hobby use.
When nothing works, I use a CCGT060204 H01 (alluminum) insert to do the job.
I use 0.4 and 0.8 mm tool nose radius but I am going to test a 0.02 mm tool nose radius because I think these will do a better job (lower cutting forces) on my lathes.
You could also try a HSS tool, that should also give a good finish under light cutting conditions.

Have you thought of using a reamer. It is hard to match their finish using turning. I only have H7 reamers (+0.02 mm) but there are reamers for press fit holes.

You don't need a press fit for a bearing. You can also glue the bearing using lock tide.

[Iain DownsParticipant @iaindowns78295]

Well. It turns out that I am an idiot.

I started by drilling out to 14mm, but there was still seem screeching. So I checked the tool height and it was a little under. I fixed that and, once I'd worked out that the best speed was around 1000 rpm, I got a good finish.

The lathe still turns to be narrower at the chuck end but is 15 microns or so better. I've tuned the outside with some emery and it's within 2 microns along the length. The bore is good enough for a 'light press fit' at both ends.

Huub I'm using the CCGT060204 (aluminium) and it's pretty much all I use for normal cutting and boring – HSS with zero rake for bronze and brass, though and I have some very small pieces to turn (2mm dia) which I will probably use hss for.

I want a tight fit for the bearings to make sure concentricity is good. If you have a gap for loctite (I use 638 for bearings) then there is the chance of it being a bit off.

I don't think I've finished setting up the lathe, but I've other things to get on with in the short term.

Thanks for all the advice.

Iain

[HuubParticipant @huub]

Ian,

Good to hear you have things working for you.

I have checked the minimum turning diameter for my 12 mm boring bar (S12M SCLCR06, CCMT060204 insert) and that is 13 mm.

Regards,

Huub

[Howard LewisParticipant @howardlewis46836]

Glad that setting the sharp tools to centre height has solve the finish problem.

So when time allows bvack to iterating taking out twist and aligning the Headstock.

By the time that you've finished, it might be better tha when first received!

Howard

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