Member postings for old mart

The guard might have enough internal clearance to just allow it to be moved rearwards the small amount necessary. I'm certain any sensible modifications would be allowed by ARC, they are a very good company. Phone them up and put them in the picture first.

You need to remove the splash shield and find out if there is a possibility of modifying it for the clearance required. It certainly looks like a small chamfer would do the trick, which could be sealed with a welded on plate, or even glued on.

Edited By old mart on 02/08/2020 15:42:26

I would try to rig up a hose from a vacuum cleaner while turning brass, I think it is even worse than cast iron.

Starting the thread in the lathe has the advantage of being perfectly in line, so if you have to finish it by hand in a vice, you know the thread will never end up drunken.

That design could easily have been compound.

An adaptor plate to fit this chuck to the mill bed or rotary table is in my list of things to do. The lightweight 6" four jaw independent Toolmex which was also NOS had the Myford thread originally, but soon was modified to front mount to fit directly in place of the very poor worn out Pratt on its backplate. As the 6" rotary table has four tee slots, that chuck can have a dual purpose.

A year or two ago, I bought a 4" Pratt Burnerd three jaw scroll chuck on ebay. It was not a size that particularly interested me, but the price was remarkably low, especially as it was NOS sold as used. It has both sets of jaws, and during lockdown, I chanced upon a 6" backplate with the Smart & Brown 1 3/4" X 8 W thread. Having a small chuck has its advantages at times, so I have married up the pair. I will not be reducing the backplate diameter in case a four jaw independent happens to catch my eye, there are holes to mount three different chucks already in the backplate. I wanted to fit the spindle thread lock to the backplate, and as the chuck is small, the mounting of both became a problem. The chuck had the common rear mount M6 threads, but rear mounting would interfere with the lock, so a modification to front mounting was the answer. I like to have a loose fitting register to enable fine adjustment of three jaw scroll chucks, but I also like to play safe with six bolts rather than three. There is plenty of room in a chuck to have six mounts, I already have Pratt chucks with both front and rear mounts from new. The procedure starts by mounting the chuck on a rotary table and lining up the existing holes and drilling them right through the body. Care has to be taken to set up the chuck so as not to risk drilling the jaws of the chuck holding the one being drilled. It pays to check carefully where the holes will go to miss any mechanism. I had a scrap 4" Pratt with front and rear mounts in it to compare first, and the hole spacing is 60 degrees. After drilling the holes 6.6mm, the chuck was turned round and realigned to Counterbore for the SHCS, which will be cut down 60mm length. The chuck had to be dismantled and washed after modifying

Edited By old mart on 01/08/2020 20:02:22

There were several versions in the griptru theme by different manufacturers, certainly if you are rich, you can buy a Bison or a P B. The types with four adjusters are much easier to use than those with three.

A long time ago, I was an instrument mechanic working in aircraft stuff, and we had a supply of shellac in flake form which was dissolved in methylated spirits, (the undyed type) as we required it. It was used to seal small screws and the like.

Looks like an AA alkaline cell to me.

Be aware that the angled tip style will tend to cut sideways a bit, owing to the blade being most flexible from side to side. Try to avoid extreme depths. A possible way around that could be to do most of the depth with a square tip, and then turn the blade round to use an angled tip in the other end for the last bit.

Edited By old mart on 24/07/2020 20:16:31

£66 for a Colchester part, it must be the cheapest ever.

Theres nothing wrong with Alan Jacksons spacers, except they are hard to make, I shall be making a pair of similar ones to grind jaws of a four jaw independent chuck. The method differs in that only one jaw will be ground at a time, the spacers tension the jaw to be ground between the adjacent jaws. I will endevour to set the position of each jaw in turn to the same radii.

Edited By old mart on 21/07/2020 20:43:44

N D I Y , there are two other options for accurate workholding, soft jaws, and the griptru type of chuck. I use both methods. My take on the poor mans griptru with the reduced register between the backplate and the chuck is present on the chuck in my photos in this thread. What cannot be seen in the photos is the presence of three rear mount shcs, giving six screws hloding the chuck on. This method is frowned upon by some .

I would be wary of honing jaws, as the hone could cause bellmouthing and also just follow any radial errors. If the jaws are not pretensioned first it is just a waste of time. Even in the most accurately made chucks, the same key should always be used to tension the jaws. Any key can be used to loosen them, however.

Thanks, everyone, I'll just give them a miss.

I used to be a member of a Yahoo group, the Smart & Brown one. The groups were supposed to have been discontinued in 2019, but I still seem to see them about. Does anyone know what is happening with them?

I'm sorry, I cannot remember if the P B jaws are case hardened, it would have been obvious when I drilled them. Unless you have a solid carbide drill, don't ruin an hss, even cobalt.

If I had to guess, I'd plump for all hard, as the recent posts by people breaking teeth while overextending their jaws would suggest. The teeth break with a bang, not a whinper.

Edited By old mart on 20/07/2020 14:17:40

I started grinding the jaws for two 5" Pratt Bernerds yesterday at the museum. Doing them properly is a long tedious task. First, they have to be dismantled and cleaned, or any precision grinding a chuck full of muck is a waste of time. Then a method of tensioning the jaws is required. I chose to drill the jaws with a solid carbide drill. Tensioning rings of just the right size for each diameter of chuck are needed. The optimum diameter to set the jaws at for grinding is just inboard of the hole in the chuck body, that is also best if you also decide to do the outside steps at the same time. With holes drilled in the part of each jaw as the photo the ring is attached and the jaws tensioned inwards to grind the inside surfaces. If the outside steps are also to be ground, the jaws must be tensioned outwards. As our chucks have loose registers, the first step is to get the chuck body running true and fully tightened using the six mounting screws for the backplate. The lathe was running in reverse backgear at about 60rpm, and I set the carriage feed to move to the right (check direction in a safe position) and took 0.0005" deep passes, about three passes between adjustments. The first jaws were true in about 0.002" of cut depth. The outside steps trued up in only about 0.001" and purely by luck with the jaw settings, the whole surfaces cleaned up straight away. You could try checking the radii with a dti to get the easiest clean up.

I only got the inside jaws finished on on of the chucks finished, so I have a way to go yet. The extended nose die grinder was very good and an improvement on the straight drill that I used to use before.

Just use sodium hydroxide (lye, caustic soda) solution, about 10% WV. An easy source is drain unblocker. It also works with steel cutters including blocked hand files. You should use a little lubricant when cutting aluminium, WD40 or AC90, or paraffin/kerosine if you like smelly work.

Edited By old mart on 17/07/2020 16:34:43