Member postings for old mart

The second point is probably a typo. That is assuming the mic is digital, 0.001mm or 0.00005"

You can get electronic potting compound for this, or an acetic acid free silicone from Dow Corning.

Don't forget, that sealing will affect any heat sinks adversely.

Edited By old mart on 02/03/2020 17:10:51

Just be thankful you have some combinations that work, and mark the matching pairs to keep them together.

4 microns tir is an excellent result, when a chuck is fitted, the results will multiply 10 to 20 fold, so chasing that tiny amount already present is a total waste of time.

I always leave the mag bases clamped on to a steel girder behind the machines. The exception is the magnetic vee block which lives turned off in its wooden box, its not the thing to leave gathering dirt in the open.

It would be worth actually checking the spindle runout, but if it is 5 microns, then leave it well alone. I was lucky to get hold of a 9" faceplate cheap on ebay which I was 90% sure was a genuine Smart & Brown one. It was, and when fitted, it ran 0.0005" tir at the periphery which saved me the trouble of skimming it.

Good for them for taking sensible precautions while the risk is high.

Normally, the top part with the rings is round, but from the gudgeon pin downwards, the piston is turned oval, with the large dimension at the front to back. Slipper pistons take this to extremes by doing away with the lower sides altogether. High silicone low expansion pistons have always been finish turned using diamond tools. Older designs used to have wire wound around below the pin, and split skirts on the non load bearing side was common.

A wipe with an oily tissue before use would extend its life, or a wax polish, even.

The full profile inserts will have the correct tip radius for the thread pitch, this is an important part of the specification for threads which have to be top quality such as for aircraft fastenings. My old firm would not have ever bought partial profile inserts for this very reason. They mostly cut UNJEF threads which have a non standard root radius which is better for fatigue life. For our general purposes, the partial profile inserts will still give superior results to die cut threads, but the difference is so small that only laboratory testing could tell the difference.

My recent ebay purchases from China don't seem to have been affected, maybe I have been lucky.

Heat an offcut to dull red hot and quench in water, if it can still be filed, it is mild steel and only deep case hardening or equivalent would save it for use as a die. The best die steels used to have manganese in the alloy.

I have marked the outside of some of the chucks with the 1-2-3 numbers and the ends of the matching jaws with a vibro etcher for easier jaw changing. The Toolmex four jaw independent is numbered by the manufacturer, but the cheap and not so good Chinese four jaw was numbered by me after juggling the jaws around to get the best fits.

For the type of SS which work hardens, a sharp drill, low speed and high rate of feed will usually get the best results. Never let the drill dwell, or the rubbing will harden the surface. I burned up a cobalt hss drill on a stainless digital scale (like the calipers have) and had to resort to solid carbide.

Regarding sharpening this type of insert, I can think of two things. First, the height would be slightly lower, and second, they are probably tapered back slightly, so reducing the height would change the profile. The profile would reduce slightly, say from a true 28tpi to more like a 29tpi. This would only be true with full profile inserts, the partial profile ones are already a compromise for use with a range of pitches on non critical applications.

The Toolmex 6" four jaw I have fits easily on the 6" rotary table, especially as there are four slots.

Cycle threads, that is BSCy come in a large variety of pitches, not just 26tpi. Motalia have a number of thread charts within their site:

https://www.motalia.co.uk/

Edited By old mart on 25/02/2020 20:03:28

That Beaver you mentioned, is it really too big? These things come to bits and are much more manageable. We took the Tom senior right to bits, and there was no part that two people could not manage. Moving it from a friends place could be done a bit at a time.

I've come across this before and simply had two 12mm drawbars made from studding, one with the end turned down and threaded 3/8" Now with the Tom Senior R8 x 7/16 UNF captive drawbar, all the odd sizes are being relegated to the drill mill. You have to be careful with R8 arbors from China as some have 12mm threads rather than the proper 7/16 UNF.

 Of course, in many mills which have a 3/8 drawbar, a 12mm one would not fit in the first place. I had to ream out the spindle bore from a 3/8" clearance to 7/16" when changing to R8 from MT2.

Edited By old mart on 24/02/2020 18:32:18

Edited By old mart on 24/02/2020 18:37:59

I had to ream out a deep hole and only had a standard hand reamer in the correct size. I turned down the end and bored a slightly smaller rod and silver soldered them together. I held the reamer in aluminium soft jaws in a vise to make sure the cutting edges did not overheat and it worked. Starting with a drill 31/64" would probably work fine.