Member postings for old mart

I think you will have to explain what you are talking about, so far it doesn't make sense.

What condition is your spare leadscrew and nut? Could it be used? I recently made a new 3/4" x 5 Acme nut for a mill, and bought a tap from Tracy Tools. When I tried a test thread in aluminium, I realised there was very little chance of tapping the thread without a tap wrench with a 3 foot long handle. The tap was about 8" long with a gradual taper, and I had to shoehorn a smaller acme insert on a special threading tool just to partially produce the thread for the tap to finish, and then it was hard work. This was in leaded bronze (gunmetal).

Do try a test piece before the actual nut, you may have to tap into a slightly oversize hole. Keeping the tap straight could be made easier using a dead centre in the end of the tap, with the nut in the chuck, preferably a 4 jaw independent.

I have decided to make a totally new motor mounting plate out of a 1/2" thick piece of 6086 aluminium, 250 x 153mm, as the modern mounts on the motors are quite different from the original ones. This is slightly thinner than the old one, but stronger as it is not a casting. The alternative was a 6mm thick plate as an adaptor, which was not thick enough for threading. The drawbar is fitted which is self extracting with its bronze bottom nut, and brass washer, half nut, main long nut and a second half nut at the top. Because the drawbar nut is a larger spanner size, the hole in the pulley housing which the chrome drawbar cover fitted has had to be bored out in the mill. I will have to look for something to make a cover out of, some nylon bar might do.

Not quite the exact topic, but worth bookmarking:

**LINK**  

Thanks for the the instructions on how to post links, I will try to remember how.

Edited By old mart on 25/08/2019 18:21:30

I have just bought a VFD made by Schneider for the rebuild of the Tom Senior mill. Reading the full manual, there is a mention of an earth leakage caused by the filters fitted to it. I don't know what the value is.

I needed a crosslide leadscrew and nut for the Smart & Brown model A at the museum, and bought a new leadscrew with two nuts which was long enough to modify for the lathe. It was advertised as 8tpi, but turned out to be 3mm pitch. I told the vendor, who immediately refunded my money and said keep it. It was one of those times when hard choices have to be made. Keep looking for a hard to get item, or make the most of what you have got. I used the leadscrew, and also used both nuts for an adjustable backlash feature. On an old imperial lathe, a metric leadscrew is not a good idea, so I used the rotary table on the mill to make a scale for the crosslide with 118 divisions instead of 125. The actual error is tiny, especially if you creep up on the last bit of the size required. The backlash is set at 0.001", which makes for smooth running.

I have looked up the thread calculator, and the standard bore through an ACME nut of 7/16" by 10tpi, is 0.343". The tip of your tap should be this diameter or a little less. To verify your pitch measurements, the scale on the leadscrew handle should be 0-100 in thousandths of an inch. Holding the two leadscrews alongside each other will confirm whether the pitches match.

https://www.engineersedge.com/hardware/acme-threads-calculator.htm

I don't know how to get a link to work on this forum.

Edited By old mart on 25/08/2019 15:04:46

You could hold the shims with a couple of 2mm countersunk screws, if you are up to tapping small holes.

When the exact pitch is in question, then using a longer reference length will give more accurate results. For instance, the difference between 8tpi and 3mm pitch is only about 0.007", which would not be easy to measure over one pitch. Not so difficult if measured over 300mm, (100 X 3mm), or 12", (96 X 8tpi).

Are you sure that the leadscrew is left hand? If it is left hand, looking at it, the threads will tilt slightly clockwise from vertical. Measuring the pitch can also catch beginners out, measure an inch of thread. There should be ten pitches from the start of the first to the start of the tenth. I would think that Boxford would either use 10tpi or 8tpi, assuming the lathe is imperial and not metric.

 Don't worry about the ACME being 29 degrees and the Trapezoidal being 30 degrees, you will not be able to tell the difference.  

Edited By old mart on 25/08/2019 13:25:02

The head is looking nice now that it is finished except for the motor mounting. Mike fitted the bearings back in the pulley housing and fitted a grease nipple in place on the original button oiler. We don't want anyone oiling the needle rollers. I milled a second flat on the splined pulley holder, so that both of the grub screws in the pulley have something to grip on. I do wonder at the design, the whole pulley and motor assembly is held onto the head with four 2BA screws. The quill spindle drive splines are lubricated with a sparing amount of moly grease applied using a toothbrush. Otherwise, ordinary lithium grease is used for taper rollers and needle rollers. Everything else has slideway oil, except for the leadscrews, which have spray motorcycle chain gease. The quill spring causes a clang if it is let go, so I am getting some 7mm diameter o ring material to make a soft stop. I had put a step in the outrigger where it screws into the quill, for no particular reason when I turned it, and the bump stop will sit there.

I am just in the process of fitting a new 160mm three jaw chuck to a backplate which had another 160mm on it. I had found that the backplate was undersize for the original chuck, which had a 142mm pcd for the 8mm bolts. I had drilled and tapped for six 6mm bolts at the same pcd, giving me a little more meat on the od of the plate.

The new chuck, by pure luck has six 10mm threaded holes at a pcd of 140mm. I have a supply of new 8/10mm titanium studs originally fitted to Westland Lynx helicopters to use for mounting the chuck. Using the rotary table on the mill, I plunged a solid carbide 8mm end cutting four flute end mill through the original 6mm holes in the backplate at the new pcd of 140mm. The register had to be reduced and now is 0.010" smaller than the chuck register. I will use 8mm nylock nuts, and a little low strength thread lock on the stud-chuck threads. I prefer six bolts to the more common three when mounting scroll chucks.

The second chuck was cheap on ebay, and has both sets of jaws, which the original did not. The jaws are not interchangeable between bodies, the new one has slightly larger jaws. It is either Chinese or Indian, the only marks on it are 3000 rpm, the serial number and 160.

This debate comes up on all the forums on a regular basis, those who must have a tight register have obviously never tried any other approach. Then they tell everyone that a self centring chuck can never be relied on for accuracy.

If you are thinking about a glue approach, remember that chucks need to be dismantled and cleaned occasionally.

That joke rear brake rod brings back memories from the 60's, when I saw a 250 Royal Enfield with a non standard front brake. It had a torque arm from the brake plate to the mudguard bolts which faced backwards. To make matters worse, it had been drilled with lightening holes.

I have deliberately reduced the registers of several of my chucks to give them at least 0.010" clearance, for fine adjustment of any size work that will fit. If you are worried about the chuck moving when in use, there is plenty of room on the back of a chuck to drill and tap more fixing holes. Of course, the bolt holes in the backplate have to be slightly oversize, or they would impede the adjustment.

A tight register means there is no way that variations in manufacturing tolerances can be overcome, some sizes of work may run well, but not all.

Vic, that looks like a domestic dimmer module, try it out as bought to see if the lamp dims ok before attempting to adjust the low setting. I found that lowering the output from the factory setting just caused the leds to flicker, so I had to return it to the original setting.

I have found that the same dimmers that work with halogen lights, also work with the dimmable led lamps.

Edited By old mart on 22/08/2019 22:19:10

Tungsten is very different from tungsten carbide. I have a small supply of tungsten alloy called Densimet. The 1/2" bars make very good boring bars for TC inserts and can be turned, milled, drilled and tapped. The relative density of the alloys runs about 18, and they have a higher Youngs modulus than steel. I also have a couple of plates of the stuff, 5/8" thick and about 10" by 4", which I have not thought of a use for yet, other than an excellent high inertia backing plate.

I have a perfectly functional Tom Tom one which is ten years old. I cannot use it as it is at "end of life".

This can happen when the boss is taking visitors around. He shows them a sample, then chucks it back in the wrong hopper.