Member postings for old mart

Isn't the tape for the lathe in a rather vulnerable position? Could it go at the rear of the bed underneath the overhanging part? Just below the saddle clamps.

Edited By old mart on 25/07/2019 22:05:22

Those friction discs look a bit like sintered bronze, but if they are used dry, they are probably based on sintered metal brake pads.

I tried out all of the metric threads that the lathe can produce with the gears that I bought in conjunction with the QCGB, and am afraid that 4 worked and 5 did not. The coarser pitched of the failures led me to believe that allowing the threading dial to run two or three turns before re engaging the nuts would have probably have worked. this would take up so much time that I have to admit failure. I shall keep a low profile for a time in case they come and take me to an old peoples home.

Looking back to the third post made by DC31k, the answer is demonstrated in the OXTOOL video on you tube.

The common single phase input inverters require the motor to be set in delta. A motor in star requires a three phase 415V supply. Most modern motors are easy to change.

Two speed motors have a more complicated wiring setup, I'm sure there are experts on this forum who can solve this. Only one of the speeds could be used with a vfd, but that hardly matters.

You don't need a threading dial, just marks on the end of the leadscrew will do. If those marks line up, the leadscrew is in exactly the same position each time.

If you also start from a stop, the saddle is in exactly the same position each time.

Those of us lucky enough to have the use of a mill can make their own custom made rear toolposts, and dedicated conventional types.

One of the reasons that I have never gone the QCTP route (apart from the cost), is the slight loss of rigidity as mentioned by Brian G.

I used mine the other day when extending a leadscrew thread. The screws are to stop the threads filling up with muck. I found a secondary use for the rear hole, a lock for the rear of the saddle.

The lathe I use has no brake, it would require a long undercut to avoid tears. I did use that method some time back, when for some reason I wound the spindle by hand, zero runout on a coarse thread, probably.

Electromagnets switched by some sort of proximity indicator all set near to the pivot point.

I would try to get a plastic gear and thin it down to about 4mm, so the helix angle of the leadscrew which is acting as a worm gear has little affect.

I don't stop or reverse the lathe, I disengage the leadscrew nut at the end of the cut.

I forgot to mention that it is a good idea to make sure the thread dial marks line up with the datum line when the nut is engaged before doing any threading.

With one of those 50mm shell mills, you can get away with removing 2 or even 3 of the tips and still use it. A 1kw motor is nearly 1 1/2 hp, which will cope with 80mm shell mills, you don't have to take huge cuts every time.

Edited By old mart on 23/07/2019 15:11:38

The Smart & Brown model A that I use is imperial, with a 6tpi leadscrew. Since getting a 125/127 mod1 gear on ebay and buying a number of mod1 gears to modify to fit the lathe, it can now produce metric threads from 0.75 to 3 pitch, which covers everything I would want to do at present.

Having made a new leadscrew nut, the lathe now has close to zero backlash between the leadscrew and saddle. That is fine, but there is still some lost motion between the spindle and the leadscrew. This means that I would not dare to keep the nut engaged and simply reverse the motor at the end of every cut.

I disengage the nut every time, the same as with imperial threads.

Impossible, it cannot be done, I hear you scream, hogwash, I say in reply.

A stop for the right hand side of the saddle is required if threading towards the chuck, or the left end if threading away. Set the stop a few thread pitches away from the start of the thread and back the saddle up to it at each pass. Choose a number on the threading dial and use it each time. The spindle and tool tip will synchronise every time.

I recommend using the same number on the threading dial every time as different makes of lathe have different numbers on their dials. The S & B that I use has 24 numbers, and I have a choice which other people would not have.

Acme thread angle is 29 degrees and trapezoidal is 30 degrees., I doubt if a threading dial gear would notice the difference.

It looks like a great demonstration model for teaching restoration to the younger club members.

Otherwise it could be a useful boat anchor.

I have parting blades in 26mm and 32mm size, from 1.6 to 5mm wide. I wouldn't use the wide ones for parting, only grooving as the lathe isn't really stiff enough for parting, especially with steel.

I ruined one end of my Kennametal 26mm by 1.6mm blade when the work moved in a three jaw chuck. A four jaw independent chuck is much more secure.

Remember to check your jibs for tightness, and always lock the saddle when parting.

I made a dedicated rear cut off block to hold 26 and 32 blades which bolts directly to the cross slide, with the blades inverted. I also added a rear saddle lock as the cutting forces are upwards. This is much stiffer than using a normal toolpost. 

I would never part off dry, soluble oil from a squirty bottle for steel, and WD40 or similar for aluminium. 

A great advantage of using the GTN inserts is that they are available from several sources, the best I know of is Korloy. I have some in 1.5, 2 and 3mm wide. 

Edited By old mart on 23/07/2019 14:01:45

Edited By old mart on 23/07/2019 14:09:56

In our fitting shop at work, we had a 2 foot square black granite 4" thick just sitting on a sheet of rubber directly on the bench. It was tested every year and given a grade A every time.

The work hardening aspect is interesting. Copper work hardens by stretching, so how much smaller do you have to make the boiler for it to be the correct size after testing?

The main thing wrong with Myfords are their mystical properties which lead to inflated prices.

Edited By old mart on 22/07/2019 14:06:39

You don't need anything too special for home workshop use, the 2 foot square cast iron table I bought has a brass label on it "not for inspection use", but the 0.0005" error it has is more than good enough for hobby use.