Myth Buster?

[Paul KempParticipant @paulkemp46892]

Was doing a little job this afternoon for a mate extending 2 keys to fit in a lock in a thick door. Needed to make a couple of extensions an inch and a half long to braze in. As I was turning the extensions down it rang some bells on various comments I have seen on here re unknown material quality (stuff from scrap bins and DIY stores) and brazed carbide tooling.

The steel was an offcut of 6mm B&Q steel from their metal racks bought for a fabrication job ages back, still has the ripped bar code label on the end!

I turned it down to 5mm over 1" (so length roughly 5 times diameter) but total projection from the chuck 1 1/2". Used a brazed tip tool sharpened on a green grit wheel without further honing or polishing and no tip radius to speak of. Speed was 500rpm (no science, too lazy to change) and feed around 0.003" per rev.

As there wasn't much to come off depth of cuts was 0.005". Surface finish was perfectly acceptable although not a mirror finish, taper over the 1" was maybe half a thou on one, which for a key shank was niether here nor there and the other came out parallel as close as I could measure.

So for the doubters it is possible to get a reasonable finish from "odd non graded" material with brazed carbide tooling even on small diameters with a long overhang. These tools are as cheap as chips and you can grind them whatever shape you like.

Paul.

[Paul KempParticipant @paulkemp46892]

B&Q steel and Brazed Carbide Tools

[David George 1Participant @davidgeorge1]

Hi Paul I agree. The brazed carbide tip tools need grinding from new as usually there is insufficient clearance and wrong shape to get a good finnish. I use them for roughing out and braze my own if I need a special shape or type of cutter. As for the steel from B and Q if you just need a bit of steel without any special property's no problem.

David

[IanTParticipant @iant]

I have a wide range of materials in my 'scrap-box' accumulated over many years. A lot of the steel is free turning (leaded) but sometimes it's not. It's all potentially useful.

It quickly becomes fairly apparent if something is not going to give a really good finish, so if I need one, then I mark the 'poor' piece with a file, put it back in the bin and look for a better bit (or worse case purchase something).

However, there are lots of times when I'm not bothered if it won't turn that well and I just get the best finish I can. I take any bad tears out with a file (normal caveats – use a handle, great care etc) and usually the finished job is quite good enough for the job in hand.

Last night I needed a simple 3" 'adaptor' rod (to fit a DTI 1/4" hole to the 8mm hole on the stand). I turned a spare length of 8mm rod down to 1/4" at one end and it was pretty rough – but touched with a file and it was quickly done. A spot of paint on both ends will remind that I've made it for a reason (in case it ever gets mixed up with other off-cuts on my bench).

All done of course with simple HSS tooling – which if it's sharp will give as good a finish as you are likely to get. Some materials may not be very free-turning but they are not usually hard either.

Regards,

IanT

 

Edited By IanT on 18/11/2019 10:24:26

[SillyOldDufferModerator @sillyoldduffer]

Posted by Paul Kemp on 17/11/2019 20:58:50:

So for the doubters it is possible to get a reasonable finish from "odd non graded" material with brazed carbide tooling even on small diameters with a long overhang. These tools are as cheap as chips and you can grind them whatever shape you like.

Paul.

Only when you know how! I stand by my advice that it's better to avoid unknown metals and difficult materials. Double avoid if you're a beginner with a small lathe who hasn't learned tricks like grinding brazed carbide yet…

Dave

[IanTParticipant @iant]

For a "Learner" – I'd certainly agree Dave, get some free turning steel (from a reliable source) and get to know your new lathe.

It will help to eliminate one of the many possible causes of poor finish when first starting out. However, once you have achieved a good finish, you should begin to be able to diagnose (or at least recognise) basic problems as you come across them, because you have probably come across them before as you've practiced your turning.

I was just making the point that you don't need certified materials for every job and that simple HSS works perfectly well most of the time. Others here have different preferences and if you are building a specific project (which will involve a lot of time invested in it's production) then it certainly makes sense to use good quality materials. But that isn't always the case in my workshop and having a good "scrap box" is not only economical but also convenient.

Regards,

IanT

[Author]

Posts