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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: Elliott Omnimill backlash
01/09/2019 17:25:41

The acetal nuts will be more forgiving of leadscrew wear, so they would be a good way to start the renovation.

I have recently done some work on a Tom Senior X axis leadscrew which is 3/4 X 5 ACME. Firstly, I extended the thread by about 4 inches at one end to allow the fitting of two nuts for backlash reduction. Then I had to rework the entire length of thread to match the wear in the centre part. There was no visible wear, but having adjustable backlash without attending to the wear variation was not an option. I was single pointing and using the travelling steady on the lathe to get the insert to just rub the flanks of the most worn parts, to cut the less worn areas to match. It is very easy to line up the tool when the thread pitch is so coarse, so the work was done in several sections, and on both sides of the thread. It has been quite successful, the leadscrew runs right through the nuts smoothly without any discernible backlash, although I have not tested it properly yet. The old nut had about 0.030" backlash and looked like a vee thread, there was no flat top of the thread left.

Thread: Is the price of this model boat at all realistic
01/09/2019 16:41:48

The delivery is free! wink

Thread: Help choosing a Chinese lathe please
01/09/2019 16:37:03

There is an excellent web site dedicated to the small Chinese lathes, showing how to improve them and much more: **LINK**

Thread: countershaft bearing replacement
01/09/2019 16:25:23

Oilite type bushes are easily available on ebay. They can be bored on a lathe without compromising the porosity, but reaming should be avoided.

Thread: Not Your Modern Lathe Tools
01/09/2019 16:21:10

I tried some Bovril some time ago after not eating any for many years, and was surprised to find that it is made by the same process as Marmite is. It is now suitable for vegetarians, but tastes exactly the same as the old beef formula.

Thread: Loctite minefield
31/08/2019 21:52:48

Loctite 290 is a useful one to have for threadlocking. It is suitable for use on many threads after they are assembled as its very low viscosity allows it to penetrate by capillary action. It isn't likely to work on nylock nuts, or good fitting countersunk screw heads, as they may be too well sealed. It is a lower strength type, safer on small thread sizes.

I recently used 620 sleeve and bearing fit on joints which were likely to lock prematurely if 601 or 638 were used. It is just as strong, but much slower setting.

It is always best to make sure that threads are degreased first if Loctite is to be used, but once cured, most grades are unaffected by oil. Temperature resistance varies, most grades are ok below 300C.

Edited By old mart on 31/08/2019 22:00:41

Thread: Lathe steady position
30/08/2019 17:22:26

I would try testing what would happen if the front hole in the steady was repositioned. Looking from the chuck side, the steady minus the front screw could be pivoted until the vertical finger is directly above the spindle axis. At this point, the horizontal finger should be checked to see if it is in line with the spindle in the horizontal axis. If those two positions can be achieved, then the front screw position in the steady can be remachined. The new hole at the front of the steady will be further from the edge where there is plenty of meat.

Thread: Tool post project
28/08/2019 20:50:33

Taking your design to extremes, assuming all your tools are the same size, would be to put the round groove directly in the top of each tool. It could be done with solid carbide bullnose cutters, although the ends wouldn't stay sharp very long.

Thread: Home Made "Inserts" -Feelin' Groovy.
28/08/2019 20:40:49

I had the work shift slightly in the chuck when parting off, and it destroyed one end of my Kennametal 26mm blade which holds the 1.6mm inserts. I am very careful with it now, only one end left and 7 new inserts which only fit that exact blade. I try to avoid parting off in a three jaw chuck, four jaw independents are much more secure.

I always lock the saddle when parting or grooving.

Edited By old mart on 28/08/2019 20:44:52

Thread: Start of Tom Senior refurbishment.
28/08/2019 20:17:53

Today, I thought I ought to check whether my conversion to R8 has been up to scratch. With the er25 collet holder nice and tight in the spindle, using Vertex and Cutwel collets and trying 6,10,and 16mm shank endmills, the runout was 0.0003" tir on each size. Then I tried out my Osborn Titanic II, with 16mm, and 1/4" shank endmills and got 0.0005" tir on both. All the careful setting up of the spindle parts and the lower bearing outrigger has paid off. I had been worrying about how the two halves of the spindle would run, especially as the SKF lower taper roller and the Timken upper taper roller ran on different halves of the spindle. One drill chuck runs from 0.002" to 0.004" and the other larger 16mm one runs 0.004" @ 16mm, dropping nicely down to 0.001" at 6mm. The self extraction with the drawbar works very well, just 1/4 turn between pulling and pushing.

Not everything is quite as fortunate as that, however, I found out that my boring out of the motor pulley isn't deep enough, so it has to go back up on its mandrel for another 14mm of bore.

Thread: Home Made "Inserts" -Feelin' Groovy.
27/08/2019 17:34:40

Sorry, I don't understand when you say the cutting part is to the right, (picture 5). As for chuck clearance, what about the SHCS sticking out? I also cannot understand why the steel should go blunt so quickly in brass. Have you tried a file on it after tempering, if the steel is low carbon mild steel, it will still be soft after any heat treatment.

Edited By old mart on 27/08/2019 17:36:18

Thread: 0.300" & 0.400" 28TPI Tap
27/08/2019 15:35:06

At the museum, having had many donations of tools over the years, we have many taps which were made for specific jobs in industry. Many only have factory code numbers and can never be identified, and others which are usable at first glance, have + or - tolerances added, which could be disastrous. My favourites are a set of three 0.7" buttress thread taps, they look wonderful, but I cannot think of a use for them.

Thread: Home Made "Inserts" -Feelin' Groovy.
27/08/2019 15:22:37

If the ground flat stock is gauge plate, it is the equivalent of silver steel. I would try hardening it, polishing it and then heating it very slowly from the other end until the tip area is light straw, before quenching. After tempering, finish hone with a fine diamond lap. If the dimensions allow, grind the end so that the plan view is biased to the right, yours is to the left, which is not so well supported by the groove in the holder. So far, I haven't needed anything narrower than 1.6mm, the width of my smallest carbide inserts for 26mm blades. I'm not sure of the best profile for brass, it is a matter of trial and error.

Thread: Taper Turning using set-over attachment in tailstock
26/08/2019 20:55:24

I'm sure you know that the measuring equipment must touch exactly on the centreline, and this also applies to the tool height, internal and external.

Thread: QCTP problems
26/08/2019 15:18:51

Got it, the first time I looked, the "QC" was black and I ignored it. Now it is blue, must be magic!

26/08/2019 13:55:15

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

Thread: ACME thread identification question.
25/08/2019 22:34:43

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.

Thread: Start of Tom Senior refurbishment.
25/08/2019 18:41:03

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.

Thread: ACME thread identification question.
25/08/2019 18:19:55

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

Thread: Current leakage om CNC
25/08/2019 16:33:34

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.

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