MachinistBlog.com

This is for "Paddleduck John" – also posted under his BLOG:

Hello John and many thanks for the time you have given us, which of course, is in addition to the time you took to make the plans and the BLOG in the first place.

Where should I have posted these comments? I’ll put them here, and maybe also in a forum.

We made the jig exactly as you described, and the plate is really tough “hot rolled” thick steel.

We do face the webs before parting, so there is one nice square face, and one groovy dishy one, and we initially used the jig in the way you describe – “upside down” – peg down between the jaws of the post drill vice. Then manually guided the drill into the holes in the thick steel plate of the jig, and down into the web.

Which way up should the web go? I guessed good side down – where it will sit on the drill vice squarely. We didn’t face the bad side as we couldn’t see a way to hold it. Your pot chuck idea is new to us, and perhaps we could make one, and use it to make new webs, but I don’t understand what the benefit would be beyond cosmetic. (that’s just a literal statement of my ignorance – not a contradiction of your advice!). In addition, since parting is such a noisy and stressful process, the prospect of putting my head near the lather through four more of them is very daunting.

Later on when our post drill-and-jig-upside-down method proved inadequate, we dumped the jig, and used the milling machine'’ table to drill accurately.

We are slitting with a hacksaw, and after the web is shaped, and I have to say it’s a carve-up. Not straight, not central, and not consistent between webs. I don’t know how we would do better. But we thought this wasn’t important – what seems to be important is that we make a gap to allow the straight, parallel sides of the holes to pinch on the shafts, thereby holding them in correct registration.

You say: “Hopefully, by using the jig, all holes should now be square.”

The central issue is that, simply, they ain’t.
And we don’t know why nor how to fix it.

We are using steel as recommended. We could use brass, but since it’s softer, I would have thought it’s more prone to allow deviations from true. The parting off could be more fun though…

Your offer of a visit is very kind indeed John, thank you. However, we live 150 miles away which is a six hour round trip, not including any “shed time”.

Perhaps the answer lies in tramming – I’d never heard of that phrase before. We did check that the quill was true – or seemed to be – but thinking about it, it was very crude – putting a rod in the chuck, and assessing its squareness visually, against a set square placed on the bed.

Another engineer suggested making the crank with the shaft all in one piece, glueing iti n place, then removing the unwanted parts of the shaft. I can see how this would true up the shaft segments, but the idea of relying on glue to hold a shaft in alignment in a hole which isn’t true seems very dodgy, and also, removing the unwanted shaft segments would seem far from trivial. In any case, it would not help us with trueing up the big end segments of the crankshaft.

We’ve also considered using square rods in place of the webs, and doing away with some of the bearing blocks to give us more room for a more chunky design.

Also, as I mentioned, cross stitch is looking very attractive.

If you have anything to add, John, we’d love to hear it, but if you’re out of ideas, then elt me thank you once again for all the time you have given us.

Best Wishes,
Chris

An update in case anyone else has this problem.

rleete – thanks but this is not correct.

I spoke to Axminster, UK dealers for this machine. The spindle lock works through a pinching action between two profiled blocks – one behind and one in front and both slightly to the right of the spindle. When you turn the handle, they pinch together, biting on the spindle, preventing it from moving.

Apparently, it's quite common that the threaded shaft is a little too long to get enough bite. Placing a couple of washers on the front of the shaft just bejhind the handle, effectively shortens this shatfs and allows more bite. We haven't tried it yet, but it seems to make sense.

Chris

Thank Rleete!

Chris

More misery, folks, which our Sieg X2 Super mill, which I'd appreciate your help with.

Our mill has a "spindle locking lever" which doesn't lock the spindle. We can turn it indefinitely, and it sort of bites but doesn't lock the spindle. When we bought the machine second-hand, the pin for this lever had fallen out, and we wonder if something fell out which we didn't replace – a ball bearing, perhaps. Anyway, please tell us how this spindle SHOULD operate, and if you have ny ideas about how to diagnose and fix it, those would be appreciated too. Right now, everything we mill is wrong in some way, and it's getting a bit tiresome.

Thanks,

Chris

I agree with Rob that the most likely cause of your problem is probably flexion of the parting tool, followed closely by a misaligned tool, followed by rotation of the tool holder holding the parting tool. You want to extend the parting tool only enough to make the cut to center and be sure you align the tool to the chuck's face so it is at a right angle to the work. You can add a brace to be sure the tool holder does not rotate, then part as close the chuck as possible. Be sure the tool is sharp and use cutting oil and a positive feed.

If you are using a small lathe then look into a rear-mounted parting tool holder. It is a vastly more rigid setup than a front mounted holder in a quick change tool post.

If you can answer Rob's questions it would help us to be more helpful.

Mikey

A forum search found nothing on this, so here goes.

Hi, we're new to machining but we have a problem with our parting tools. Even new ones tend to (a lot but not always) part off leaving a dish or a dome on the working faces. The tool is set perpendicular to the lathe axis, the tool is centred, and the cross slide is locked during parting. Any ideas why this happens?

Many thanks for any insights you can offer.

Chris