Retro Randa Mini-Lathe escapades

[SteveA]

So after everyone's help in my "should I buy it thread" I've got the Randa / Grayson thingy installed, wired and running.

I could do with some tips on operation (see below)

First job was just cleaning support material off a 3d printed wheel - easy enough.

I must say I'm struggling somewhat with my own / the machine's capabilities.

I have one of those chinese mini-screwdriver sets with multiple bits for taking apart electronics. The shoulder on the bits stops them being used for screws more than 10mm or so deep (lots of screws in electronics), So I thought I'd have a crack at turning some of the shoulder down to a more sensible diameter.

I'd expected this to be easy, as the bits are tiny and (I assumed) made of cheese metal.

Unfortunately, it kept pushing the tool under the work, even though I thought I'd centred it.

Also just wore the tips off a couple of HSS tools and didn't really cut.

Wonder what I did wrong?

Next I'll try something which I guess would be more forgiving for beginners like a knurled thumb screw in brass or ally

I'm also keeping an eye out for a treadmill locally. So I can try a variable speed conversion.

 

[Misterg]

I'd expected this to be easy, as the bits are tiny and (I assumed) made of cheese metal.

Hi,

The bits could well be as hard as hell!

Better try with some aluminium to get the feel for things. It's tempting to use "scrap" but unless you know what it is, there's no guarantee that it will machine nicely. IMHO it's worth buying a few lengths of 6XXX aluminium from ebay or the like as 'known good' stock and use that to gain some experience / confidence - likewise some free machining steel (EN1A-PB).


IME the positive rake, polished carbide inserts work very well for a small lathe, and eliminate (or postpone) the lottery of the tool grinding learning curve but that's a whole other can of worms!

 

[Kram]

Screwdriver bits are likely to be hardened at minimum and a chrome steel, very tough for a small lathe to turn! Any steel with chrome in it, will be better with carbide tools if you want decent life.

If you search ebay for usacut55 16mm, that is one of the nicest steel grades I have found and it still has the strength to be useful - unlike en1a. It can be hardened. Turns a bit like brass, good for a small lathe.

IME the positive rake, polished carbide inserts work very well for a small lathe, and eliminate (or postpone) the lottery of the tool grinding learning curve but that's a whole other can of worms!

Wrong tool for the job, on steel they last only seconds. Small finishing grade ccmt0602 are a better choice, ones with a very low minimum depth of cut. They will also be much better at breaking chips which is half of the challenge.

 

[Misterg]

Wrong tool for the job, on steel they last only seconds.

Not in my experience - I find that they (CCGT060204 specifically) cut steel very well at the sort of cuts that a small lathe will be making .

But like I said:

that's a whole other can of worms!