Using the Britan Repetition Lathe

[Anonymous]

Dave,

Thanks for the confirmation that I've understood your advice. I've got quite a lot of tools ready ground by the previous owner(s). I've also got a few 5/16" tool blanks, and I've bought a few more for stock.

I didn't have any problem drilling 20mm deep with a 3mm drill in one go; may be I was lucky. Then again Delrin is one of the easiest plastics to machine. I did open the collets a few times before stopping the spindle, by accident. All these jobs involve pushing the part up against the backstop before closing the collet; I didn't fancy doing that with the spindle running. I'm rather attached to my hands, and I'd like to keep it that way!

Regards,

Andrew

[David Clark 13Participant @davidclark13]

Hi Andrew

We put items in the collet while it was running.

I still have all my fingers and thumbs.

Not a good idea if the work is sharp.

You can push the item in with a revolving stop and tighten the collet.

regards David

[Anonymous]

David: Thanks for the information, but I think I'll be coward and stick to stopping the spindle to change parts. I was using a secondary split bush to hold the parts, which tends to fall out if the spindle is still spinning. I can always include the time to stop and start the spindle in my quotes.

Regards,

Andrew

[websnailParticipant @websnail]

Posted by Andrew Johnston on 09/02/2013 11:15:20:

but I think I'll be coward and stick to stopping the spindle to change parts…..

Don't worry, one day you will.

Round or hex is fine. Square section can be a pain though, so stop the spindle for that.

Stick a bit of material in a tailstock collet and use that to push it back to the back stop.

Re Bushes falling out: You're machining dry, so lose the front guard and you're have all the room to catch both the bush and the work peice.

[Anonymous]

I am running without the front guard. I see what you're saying about pushing the part in with the tailstock. But it doesn't help push the secondary collet into place? For the second part I machined to length (31mm) I seemed to be on the limit of adjustment for the backstop, with only a couple of millimetres of the part sticking out of the collets.

The lathe came with a special red plastic tea stainer, specifically for catching small parts.

Regards,

Andrew

[websnailParticipant @websnail]

Hi Andy,

There are three ways to put material to a stop in a Britan.

1, A bung in the far left of the spindle, through which, a bar is pushed into the spindle (with the business end machined to fit the job) and held in place with a cross screw.

2, A billet of ally, held in the back of the collet by a small cross screw (locating in one of the collets 'fingers&#39. This would be tapped M10. Make up lenghts of M10 studding, turned smaller than the job, a lock nut finished the 'stop'.

3, Tail stop stop. The job is held in the part closed collet. Bring up the tail stock stop, close collet. We used 3/8" ally. You might need a hole in it for any pip on the material.

Split bush. Depends upon what it's tighter in/on, the collet or material. Put it in/on the tighter one first. Plastic comes in in wide tolerances. Use to drive me mad, going along nicely, get another lenght from the bundle and………..problems.

Precision ground plastic solved most problems though.

Tea stainer. Only ever used one of those when we used neat cutting oil instead of sudds. Fingers or a selection of two steel hooks for me.

Regards

Dave

[Anonymous]

Dave: Thanks for the summary of stop options. I've been using aluminium split collets, although I did have to remake one, as it wasn't holding the plastic tight enough. I wondered why the parts were coming out short! I know what you mean about plastic; I'm using 12mm nominal diameter, but it's nearer 12.3mm. The parts fit into counterbores made with a 12mm slot drill, so have to be machined down, a real PITA. I did all the size reducing in the conventional lathe, easy to set up and then lock the cross slide. The longer spacers only needed a short length each end machined down, with no length tolerance, as long as it was more than 2mm. For the shorter parts I faced off and machined to diameter before transferring to the Britan to finish to length and drill and tap the central holes.

At least if the client asks for more jigs in the future I've got all the fixtures, assembly tools and collets made ready and waiting.

Regards,

Andrew

[David Clark 13Participant @davidclark13]

Hi Andrew

Why not use a top hat home-made collet.

The lip of the top hat goes against the Britan collet and the plastic goes against the inside of the top hat. Because you are puching the plastic into the chuck it pushes the collet in too. You could still have the spring loaded backstop pressing against the component (put a hole in the back of the top hat) but is does not need to be used as a backstop.

Regarding different sizes of plastic, keep all the components made from one bar together and the diameters should be the same.

If they vary, select components of the same size into batches. Quicker than turning down.

regards David

[websnailParticipant @websnail]

Posted by Andrew Johnston on 14/02/2013 11:37:56:

At least if the client asks for more jigs in the future I've got all the fixtures, assembly tools and collets made ready and waiting.

Yep that's the way to work. Keep them together. On jobs where we needed to get creative, I'd write the tool postiions down, along with the method, ready for the next time.

We would aim to set up from scratch in 1 hour or so, including tickling the tools on the off-hand grinder. If we were 'chasing tenths' then it would take longer.

The top hat collet that David says, is a good idea. Only you know what you need, it's part of the art

More than one way to skin a cat

Dave

Edited By websnail on 14/02/2013 20:54:33

[David Clark 13Participant @davidclark13]

Another way to skin a cat.

When you do any setup for production, complicated or not, take a digital photo of the setup.

We always kept a book with a drawing of the setup and the tools etc.

Digital camera would be much quicker.

regards David

[Anonymous]

The top hat collet is a really good idea, thanks! For short parts it'll save me mucking about with the backstop.

One of collets I have was clearly made by the previous owners, using a similar principle. It has a larger hole in the front of the collet, but only a small hole at the back, so it can only have been used for holding short parts. Or parts with a thin spigot on them I suppose.

Regards,

Andrew

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