Face turning Bronze castings – strange surface finish

This topic has 31 replies, 18 voices, and was last updated 27 March 2020 at 19:48 by Tony Pratt 1.

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19 March 2020 at 09:33 #458118
Pete Rimmer
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@peterimmer30576
If it's loose headstock bearings you could put a bit of load on it using the tailstock centre. Just get a bit of scrap ally or something and pop a centre drill hole in the face of it with your cordless. Grease up the flat face and the centre drill hole and use it as a rotating pressure pad.
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22 March 2020 at 19:47 #458962
mike robinson 2
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@mikerobinson2
Firstly many thanks to everyone for taking the time to respond. I have used a lathe since I was 16 as an engineering apprentice and I am 66 now. New things are not always better and the great news is a sharp HSS tool has solved the problem. The surface finish is good and smooth (flat) even on the interrupted cut.

Perhaps I should have added at the start, my Super 7 was a fully re-furbished machine from Myford about 3 years ago, the lead screw is good, the cross slide feedscrew is new and cross and top slides are set well. I was able to complete by Quorn grinder without any issues.

The insert by the way was from JB Cutting tools with a brand name of "TaeguTec" ,and I have never had an issue before, seems bronze is more troublesome than I remember. I will try to post a picture of the HSS test cuts shortly

Thanks again to all for the support !

Mike
22 March 2020 at 21:15 #458978
IanT
Participant
@iant
Hallo Mike,

I don't use inserted cutters for this kind of work, so when facing this piece I would be using a HSS tool with zero (or negative) back rake.

Anecdotally – I recently tried to face a bronze casting with the Diamond tool-holder that was already fitted (being too idle/stupid to change it) and for a few seconds all was well – and then the tool dug in. My old S7 has a good deal of backlash present in the feed screws – and frankly I should have known this was going to happen. A sharp, zero back-rake HSS tool cut the casting with no problems.

If your machine is fairly 'tight', then using an insert (with positive rake?) might not dig-in quite so badly – but I wonder if something similar was going on?

Just a thought…

Regards,

IanT
27 March 2020 at 18:15 #460238
mike robinson 2
Participant
@mikerobinson2
Crazy times, crazy week. Apologies for taking so long to upload the photo showing a much better surface finish when using a HSS toolbit Vs insert tooling (which has never been an issue before)

Least I am back on track and 2 more to go….

Thanks again for all the advice.
27 March 2020 at 18:37 #460241
old mart
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@oldmart
Try the aluminium versions of your carbide inserts, they are much sharper and will work like the hss.
27 March 2020 at 19:17 #460253
Nigel McBurney 1
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@nigelmcburney1
Why waste your cash on carbide inserts,HSS correctly ground as I said earlier can give very good finishes and at a very low cost ,its choosing the right tool for the right job, and most hobby work only needs HSS though it does require a degree of skill .
27 March 2020 at 19:48 #460265
Tony Pratt 1
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@tonypratt1
Posted by Nigel McBurney 1 on 27/03/2020 19:17:40:

Why waste your cash on carbide inserts,HSS correctly ground as I said earlier can give very good finishes and at a very low cost ,its choosing the right tool for the right job, and most hobby work only needs HSS though it does require a degree of skill .

All engineering requires a 'degree of skill'

Tony
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