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Member postings for old mart

Here is a list of all the postings old mart has made in our forums. Click on a thread name to jump to the thread.

Thread: Pratt Burnerd 4 jaw Chuck jaw alignment
22/10/2019 13:57:50

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.

22/10/2019 12:36:33

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

Thread: Turning a recess in the end of a bar
22/10/2019 12:17:25

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.

Thread: Those little screws for carbide inserts...
22/10/2019 12:07:40

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

Thread: Boring bar
21/10/2019 19:10:34

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.


Thread: Changing chucks on Harrison L140
21/10/2019 17:42:54

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:


Thread: Boring bar
21/10/2019 16:56:31

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


Thread: Changing chucks on Harrison L140
21/10/2019 16:50:49

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.

Thread: Two weeks wasted
21/10/2019 16:05:24

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.

Thread: Pratt Burnerd 4 jaw Chuck jaw alignment
21/10/2019 15:57:55

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

Thread: Two weeks wasted
20/10/2019 22:08:45

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

Thread: identify
20/10/2019 22:02:59

If it is old silver steel stock and good stuff, it will have "stubbs" on one end.

Degrease it and put it in some water overnight, silver steel is not rust resistant.

Mild steel is rarely ground, but silver steel is.

Edited By old mart on 20/10/2019 22:04:54

Thread: Pratt Burnerd 4 jaw Chuck jaw alignment
20/10/2019 21:57:16

I wonder if they were deliberately tapered to give a better fit when they are tight. You can test this theory, by turning a length of aluminium for a parallel smooth finish, and then clamping it nice and tight in the chuck. Do the jaws up slowly and as evenly as possible, and then look at the jaw marks on the bar to see how even they are. All chucks and jaws are subject to a little flexure when tightened.

I would prefer this to bellmouthing any day.

Thread: Self extracting drawbar for mill
20/10/2019 21:46:16

_igp2476.jpgI happened to notice messages and when I looked at them, one was asking how I went about making a captive self extracting drawbar for a mill. Now I have read it, the message has disappeared and the name of the sender has vanished. So I thought I had better explain how I went about this modification.

Not all vertical mills will be suitable to fit a captive drawbar to. I was lucky because there was space inside the spindle to fit a nut close to the lower end of the drawbar and also not foul the tooling.Some measuring will be necessary before any work is carried out. I cut the thread on the 7/16" en19T drawbar blank on the lathe, and put about 2 1/2" on either end. I made the bronze nut (in black) long enough to Loctite securely with a flange thick enough to not be in any danger of breaking off. At the top end, I used two half nuts for locking and a piece of threaded hexagon bar large enough to ensure that the upper locknut didn't foul the ring spanner that tightened and released the tooling. I was lucky to find a stub ring spanner with a handle of just 6" long, which is plenty. Due to the design of the mill, I had to put spanner flats on the bottom of the spindle, as there was no lock,or any way to hold it. With a minimum endfloat on the drawbar, it breaks the taper in 1/4 turn._igp2436.jpg

Thread: Two weeks wasted
20/10/2019 19:28:35

How about drilling a hole just a bit larger than the pins in a block of steel, or bar, putting that in a vise and when the job is heated up, quickly punch the pins out using a drift. An assistant would be a great help and a rehearsal before heating to get the procedure off pat.

20/10/2019 18:50:06

If you silver soldered the pins in, why can't you unsolder them? A solid carbide drill will work on even fully hardened silver steel, which it is unlikely to be anyway. Solid carbide should not be used in a hand drill as you will break it.

Thread: Problems with "The Home Shop Machinist" website?
20/10/2019 15:53:08

After being a member for several years, I managed to post my first photograph on the HSM. It now has a similar method to this forum.

Thread: DRO to vertical mill z axis
20/10/2019 14:54:16

If you aren't prepared to do some basic modifications to your mill you might as well forget the whole thing.

Thread: windoze 10
20/10/2019 14:49:18

There's yet another build coming to W10 sometime in November for the early adopters to get, but most pc's will not be forced to get it for some time.

Thread: Slideways oil
20/10/2019 14:43:24

Don't be put off by modern synthetic motor oil being thinner, the main reason why these oils contribute so much to engine life is their superior lubricating qualities precisely when the greatest wear is present, when the engine is cold.

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