Member postings for Martin Connelly

See this thread for pictures of the tool.

**LINK**

Martin

Ajohnw, the reason the tufnol gears outlast the metal gears is that abrasive particles can become embedded in the softer tufnol and so abrade away the harder metal gears. This is a common happening when soft and hard materials are in contact with each other and there is relative movement. Shaping and polishing mirrors for telescopes can be done by putting the polishing compound on a pitch lap's surface and moving the glass over that surface. The glass is removed but the softer pitch is protected by the abrasive that embeds itself in its surface. As this lathe looks like it was never cared for the lack of cleanliness that is required for this mechanism to occur seems very likely.

Martin

John and Michael, if you look at the centre portion of the spindle gear where the tumbler engages there is clear evidence of wear in the photos as presented. The ends of the teeth in the one o'clock to 5 o'clock position look like they have been stripped off.

If a new spindle is out of the question but the general state of the rest of the machine is in good condition I would suggest it is a potential CNC conversion. A spindle index pickup and X and Z axis drive is all that is required to make a machine that can still be used for turning and screw cutting. The gear driven drive train is redundant when such a conversion is carried out.

If you think this is beyond what you want out of a lathe you should be aware that by using manual data input (MDI) you can drive a CNC lathe just like a manual lathe but without using the drive train or turning handles to move the cutter around the workpiece. If you want to go further into what is available in CNC you would have the basic setup required with that setup.

If you think you want to stay away from CNC then maybe you could sell it as a machine that someone else could convert to basic CNC turning.

Martin

The dealer has probably got away with this because most motors do not run at full rated power all the time. Who, for example, has a lathe cutting at maximum metal removal rate 24 hours a day? I agree with Michael W. Always get a bigger inverter than the motor requires, it may be re-purposed or the motor replaced with a larger one.

Martin

I've had a conversation with an inspector that went:

The drawing states maximum gap of 0.5mm between the parts!.

They are touching so there is no gap.

There is a gap at the edge that is more than 0.5mm.

That is because the parts' faces are not flat, but they are touching so there is no gap.

There is a gap at the edge greater than 0.5mm.

Why is an assembly shop inspector looking at the part manufacturing drawing? What does the assembly drawing have on it?

Assemble the parts and check for leaks at pass off testing.

Then go and do that and when it fails that test come back and complain.

End of conversation.

He did not come back since the parts had already had a hydrostatic pressure test and had been passed off by the manufacturing department's own inspector. I think there are some inspectors who just love to justify their work and if they dig their heels in they take some shifting. I know one who I think was ready to claim that some stainless steel was no good because it didn't taste right when he licked it.

Martin

If you have an old hard drive that is scrap you can dismantle it and use the disk as a front coated mirror. The disk is aluminium and cuts easily with a junior hacksaw.

**LINK** for acrylic sheet

Martin

I saw a documentary that said the clipped wing improved roll rates, so that backs up JA.

Martin

Gas fuel, liquid fuel, lubricating oil, air carbon dioxide are all transported by tube used in gas turbine packages. Rather ruins the idea that tubes are structural. Then there is scaffolding as used in the UK that is 1.5 sch40 nominal bore pipe. Purely structural and not used to transport any fluids except by accident if it rains.

Tube bought based on its imperial sized outside diameter and wall thickness is specified to plus or minus 0.005", I don't know the tolerance for metric OD tube. Nominal pipe sizes are based on ANSI standards and the tolerance on OD for sizes about 2" NPS is over plus or minus 0.06" if I remember correctly. Also nominal bore pipe has a minimum wall thickness but no maximum wall thickness, instead it has a maximum weight per unit length. This is a completely different way of defining the material from that used for OD tube.

Nominal bore fittings such as tees, elbows, reducers have dimensional tolerances of 0.06" and tube fittings match the tolerances of tube of 0.005".

It is because of these two major differences in the tolerances and method of specifying size that we differentiate between tube and pipe raw materials where I work.

Martin

Sam L, pipe is available seamed or seamless, tube is available seamed or seamless. The method of manufacture cannot be used as a means of differentiating between what gets called pipe and what gets called tube.

Martin

Where I work we refer to nominal sized pipe (NPS) as pipe and outside diameter tube as tube. They are both seamless. Once we make something from the tube or the pipe either by bending it or welding fittings to it the part produced is called a pipe (or sometimes a manifold). I think this is purely our own way of differentiating between the raw materials rather than something written in stone somewhere.

Martin

I was milling some copper sheet this weekend. I was using the side of a Ø16mm 4 flute milling cutter to square up 1 edge about 100mm long so had the sheet held flat in the vice. I found that using climb milling the finish looked like it had been cut with a saw going hell for leather, not pretty at all. Went back over the edge with a small depth of cut and conventional milling and got a fine smooth finish. When set up to cut out a section to leave a U shape with the part clamped at all 4 corners with a Ø10mm mill conventional milling gave a rough cut and going back to climb milling gave a smooth finish. The point of this is that sometimes climb milling is best and sometimes conventional is best, it is all dependent on a lot of factors.

I think this item on the CNC Cookbook web site explaining climb versus conventional is worth a read.

**LINK**

Martin

I think you should check contact surfaces with some engineer's blue. A small high spot of 0.3mm may be doubled to 0.6mm at the point of the centre if it causes any angular error in the tailstock. These are not unreasonable amounts of material to remove with a file. Use of blue will let you see where there are high spots where material should be removed to maintain flatness. For this small error a milling operation may be a bit of "sledgehammer to crack a nut".

Martin

Does the height difference change if the tailstock barrel is extended out or retracted? Change like that would indicate that the tailstock was not parallel to the bed and that there may be some swarf or other debris stopping it from seating correctly. I would be wary of milling the tailstock, too easy to go too far. Less aggressive material removal may be slower but safer.

Martin

If you have a spring scale you can weigh the bit when fully immersed and the difference between the immersed weight and the weight in air will give the weight of the displaced water. The air weight divided by the displaced water weight should give density.

Martin

I have used ER11 collets in a Ø16mm shanked collet holder to hold small tools for accessing setups like this. It will not give enough clearance on very small flywheels or ones set at a small angle but is better than a full sized chuck for some jobs.

Martin

The division of a circle into radians was missed out. There are 2 x pi radians in a circle. The definition of a radian being the angle of radius r whose arc length is r. The useful part of this is that when working in milliradians a good approximation of rise or fall at a given distance horizontally is 1mm per metre per milliradian for small values of milliradians.

Martin

The shanks can be turned down in a lathe as long as the cutters are not solid carbide.

Martin

JasonB, you are of course correct about 0.707 and 1.414 and the square root of 2, I should have said 0.707 is the inverse of square root of 2. More haste more mistakes applies to everything.

Martin

Further to this 2:1 ratio in similar sized diameters for skew gears:

The angles in the example above are found from the inverse tan of 0.5 and 2 (half the speed one way and double the speed the other).

Tan(63.435)=2

Tan(26.565)=0.5

The angles have been rounded to 3 significant decimals. If they are rounded to 1 decimal you get the angles stated earlier.

Hope this helps anyone considering other possible ratios.

Martin

Here are some pictures of what I tried to explain above.

**LINK**

Martin