Member postings for old mart

Most of mine are solid carbide or densimet. I have only ever bought one, a Garant 6mm, but it cost a lot for a box of inserts as they are tiny proprietary ones. Don't think that a top quality steel boring bar is any less bendy than a cheap one, size for size,Youngs modulus for steel doesn't vary much.

It is difficult to get a good finish with any straight flute reamer, let alone an adjustable one. You will likely end up with a bellmouthed hole. I would go for a different approach, namely, boring the bush to finished size, and making it a sliding fit in the housing, (0.001" clearance), and using Loctite, 601, 638, 620 or equivalent.

Edited By old mart on 23/10/2019 19:56:50

Go for the larger one, you are unlikely to ever buy another. The cutters are not much cop, but they can be improved somewhat by touching them up with a diamond hone. I have turned the centre part of each cutter shank a few thou down so the burr left by the securing screws does not make them difficult to remove from the head. As the head will be out of balance, use a fairly slow speed.

 Never run one of these in reverse,it will unscrew from the arbor.

Edited By old mart on 23/10/2019 19:49:17

Get one like this, she won't be able to knock it over.

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Thee were some changes made when UNF was ratified, that 12/14 tpi was exactly where the change took place. UNF threads from 1" upwards are now fixed at 12tpi, unless they are UNS, which could be anything.

Also threads marked NF are now UNF.

Check out the list of topics, there are two dedicated to drawing errors. You may be able to prevent somebody making the same problems as yourself.

I've just realised that my last thread was ambiguous, when I said "it broke in half", I was referring to the insert, not the screw. The tendency to disappear is the reason I have a supply of all the sizes I use in a box ready.

If you do that, you are tensioning the jaws outwards, which defeats the whole object of tensioning them in the first place. They must be tensioned in the same direction as they are to be used.

Grinding this type of jaw would be best done individually in a vise. There still needs to be a slope on the jaws, and it would be best to try reducing the slope from the present 0.1mm to 0.05mm initially and then find out if that solves the problem.

The reason for drilling the jaws is because they have to be tensioned inwards while leaving the inside edge free for the grinding wheel, a near impossibility with four independent jaws, which is why nobody grinds them in situ.

I have a 6" Toolmex four jaw independent at the museum, and will try measuring the jaws to see what slope they have.

Something I forgot to ask is whether the jaws have been ground flat on the faces, or axially with a wheel. If the surface is curved, they will have to be checked while sitting on a cylindrical surface. The ideal diameter of cylinder would be about half the width of the jaws, with a shim to hold it on the jaw centreline.

If that 0.1mm slope is just made parallel, you will definitely end up with bellmouthing when the chuck is used, there has to be clearance in the slots for the jaws to move and all jaws have a degree of flexibility.

The last time I ground internal jaws, which are the same way round as yours, the only way to pretension them was to drill holes in them for the tensioner pins. A solid carbide drill was required to get through the case hardening.

Edited By old mart on 22/10/2019 12:43:55

I would start with a small drill making sure the tip only went 6mm deep and then a succession of end mills up to the size of the tailstock chuck capacity. Then a boring bar just small enough to increase the size of the hole until there was room for a larger boring bar to finish the job.

I have a supply of these screws from 1.8mm to 3.5mm. They may not be industrial quality, but good enough for light use. They all are standard metric coarse. I overtightened one of the early CCMT 06 ones and it broke in half, now I always use the proper torx drivers with the coloured plastic end, just thumb and forefinger tightness is plenty.

 When you drill the hole, offset it about 0.002", so the screw pulls the insert tight into the holder.

Edited By old mart on 22/10/2019 12:10:22

It is very likely, that the cost of replacement inserts for this bar would far exceed the price of a cheap Chinese bar and inserts.

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What make and model VFD is it?

That L00 catch plate could be modified to use an er32 collet system for small jobs, like this one:

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I hope you have saved the bits of the broken insert. These charts may be of help in identifying the exact type.

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If your lathe uses a L00 size backplate, (check the size) it will cost around £100 for the plate. From the picture, your three jaw is fitted to a separate backplate, but as three and four jaw chucks vary so much in registers and bolt fittings, it would not be easy to get both types fitting on the same plate.

How do you expect to stop the lathe in an emergency with only the VFD controls? The stop button is tiny.

Solving problems as you go is a major part which makes it interesting, if you don't want some bother, I suggest getting a painting by numbers book.

I'm pretty sure that nobody's checked the jaws of a four jaw independent before. Plenty of three jaw scroll chucks get tested. I would hold back from any grinding until other jaws have been tested properly.

When three jaw scroll chucks are ground it is important to preload the jaws first, which removes any backlash and tilts the jaws in their slots. Have the jaws in question been preloaded in the chuck body before testing, I think not.

Has a freshly ground three jaw chuck jaw been tested for squareness, I very much doubt it.

Edited By old mart on 21/10/2019 16:00:40

Buy her a bunch of flowers, then she will be keen to help you next time.