Member postings for Martin Connelly

10mm alloy plate would be better than 8mm to be close to 3/8", you could turn the blanks down to 3/8" if required to be exact.

Martin C

If you put a DTI on the fixed jaw and set to zero then for 45° an X axis movement should equal the Y axis movement. Eg if you move X 50mm then to get the DTI back to zero should require a 50mm Y axis movement.

Martin C

Hopper, Joe Pieczynski (Pie for short) does this frequently.

Example of turning from the centre outwards at 03:20

Martin C

Smart and Brown also use 16DP gears. Here is an original with one I made, 95 teeth.

Martin C

Wixroyd and WDS come to mind but the cost may surprise you as they sell to industry.

Martin C

The answer is it's complicated. The materials, any plating and lubrication used change the torque values required. If the threaded hole is a soft alloy, for instance, it will be stripped of its thread by the torque used for the same screw going into steel. The value we had at work for non-critical M8 fasteners were as follows for 8.8, 10.9 and 12.9 screws respectively: 25Nm, 35Nm and 42Nm. There is an additional caveat that these figures, as well as only being for non-critical fasteners, are for natural finish or light oil lubricated only, for permanent joints using nuts and bolts or studs. When the joint was to be dismantled again then the torque was to be reduced by 17.5%.

Some major connections we did we were not allowed to used hot dipped galvanized nuts, bolts and washers because over time the zinc could squeeze out like toothpaste. Sometimes we measured the resulting stretch rather than using torque to achieve a good connection. Sometimes we torqued to a value that was going to give good metal to metal contact then turned the nut through a given rotation to give the correct stretch, much as used on some modern cars.

Frequently when people use a low friction moly based type of lubricant, thinking it can't hurt, the torques used were easily able to snap bolts or strip threads. Use of these types of lubricant require a big reduction in applied torque.

Martin C

Robert and Clive, we used to use tri-lobe thread forming screws in 6mm thick mild steel. I think we got ours from Lancaster Fastenings. They were used for securing cable trays and saved time and broken taps as they were often being used in hard to access positions. It became an economically viable process when battery powered drills and nut drivers became cheap and reliable.

Martin C

Engineered Composites Ltd make GRP rectangular profiles. They may have something that suits your needs.

**LINK**

Martin C

Vasantha

Martin C

Lee, what I now do with plastic is mill as much of it off as possible before turning it to final size and shape. You can waste so much time repeatedly stopping and clearing the tangle then restarting otherwise. I can switch my A axis on my mill from stepping through to a position to continuous rotation and it comes in handy for this. Vacuuming up small chips is much easier than clearing a tangle of plastic. A recent job I did included this step and the final profiling had a step where a short stop after I was past the edge broke the tangle then the rest of the cut sent the ribbon flying in an arc like water from a hose and fell on the floor in an easy to collect heap. I took videos of this flow off the cutting tip but have not posted them anywhere yet.

For anyone who is wondering, I did not do the whole job on the A axis as, from past experience, the surface gets ripples that look like chatter if you do not get the RPM of the workpiece, the RPM of the cutting tool and the feed rate in the sweet spot. Leaving a machining allowance of 0.5mm - 1mm leaves enough for cleaning up to a smooth finish.

Here is picture of flying ribbon of swarf when cutting Oilon, this was just cleaning up the outside diameter and in the background you can see the tangle from facing the workpiece and boring the centre.

Martin C

Edited By Martin Connelly on 30/01/2023 13:03:49

It would be interesting to know if these hobs include monitoring of the induction coil to moderate what they do based on induced back EMF from the cook pot. It might prevent them from being repurposed.

Martin C

The rotation axes are about the translation axes in the following relation ship. A is rotation about X, B is rotation about Y. C is rotation about Z. The positive direction of rotation is clockwise if it is looked at along the relevant axis going from small to large positive values. This is the same as a conventional right hand thread and is referred to as the right hand rule. For a conventionally laid out lathe this means that a lathe that is rotating clockwise should be turning in the conventional turning direction, ie top towards the operator. You have to look at the Z axis from the headstock towards the tailstock to see that this is in fact clockwise. A drill in this lathe's chuck will drill towards the tailstock, ie the drill's Z position would be increasing positively relative to the workpiece, if it could move.

With a mill the C axis about the Z axis is normally turning anticlockwise and you push the drill into the workpiece by decreasing the Z axis value. To see the correct direction of rotation of a mill spindle you would have to look from the R8 socket (or whatever your mill has) towards the drawbar end of the spindle as this is the direction of increasing positive Z.

It is easy to be confused if you look at a rotational axis from the wrong direction. From the tail stock a chuck that looks like it is rotating CCW will, at the same time, be going CW when looked at from the head stock end of the lathe. It is unsurprising that these concepts can cause confusion, especially for someone sat at a desk working out what to put on the screen for a piece of software.

Martin C

PS When thread milling an outside thread from top to bottom and rotating the cutter about the workpiece you are doing something analogous to single point threading in a lathe. If you thread mill a conventional RH thread this way your Z axis is going from larger Z value to smaller Z value and at the same time the tool is orbiting the workpiece in a CCW direction. This CCW is, relatively, the same as a stationary tool and a rotating workpiece going CW.

Edited By Martin Connelly on 28/01/2023 12:58:26

CNC pipe bending machines use YBC. The vertical rotation is the C axis, just the same as it is on a milling machine since C is rotation about the Z axis. The feed of pipe into the bend head is the Y axis and the rotation about the Y axis is the B axis (plane of bend). It is a convention that matches CAD, and mathematics as well when drawing graphs. 3D graphs have the relative orientation of the Z axis to the XY plane the same way round as machine tools. 3D graphs possibly preceded machine tools and the convention used for these graphs could then become the norm for machine tools to avoid confusion.

Martin C

You can do anything (within reason) if it has had a written risk assessment carried out for the operation prior to the operation and, if required, put suitable control measures in place. Complaints about health and safety are often made by people who have not been involved in it to any degree. The biggest issue we had at work was with people who thought they could do a mental risk assessment and then do anything they wanted because of this mental exercise. They missed the written bit off and believed they could get away with it.

Martin C

It is a good idea to have a power supply rated for a slightly larger current than peak as it will be stressed if it regularly runs at its maximum output. It is possible that the power of 120W is useable shaft power and the extra current is to cover losses in running the motor. I think there have been threads in the past where the differences in motor power stated in adverts for the same basic machine were due to some vendors quoting useable shaft power and others quoting electrical input power. The latter makes the machine sound better since if your motor uses 5.6A and 24V the consumed power of 134.4W sounds better than the useable shaft power of 120W.

Martin C

It also makes sense to do this if a lathe is converted to CNC or ELS with X axis drive.

Martin C

Howard, power is volts times amps. For a 15hp 3 phase motor the phase currents will be 1/3 the current of a single phase 15HP motor at the same voltage. This (simplified) means that at full power a 1.2kW single phase motor at 240V motor will require a current of 0.5A in its single phase wiring. A 1.2kW 3 phase motor fed 240V (line to line as in a VFD) will require 3 currents of 0.5A/3 to give the same 1.2kW at full power. The current to the VFD will be slightly higher than the single phase current due to losses in the VFD.

Martin C

The effect of a flywheel large enough to reduce the acceleration of a single phase motor may be a large current draw until it is up to speed. This is not great for the wiring or the motor unless it has all been designed for such a system. Then when power is cut off the system will act like a generator until the motor is at rest so you may need a system designed to dump that energy into a resistor (a DC brake in effect). Turning a large lump of metal may cause the same effect, they can take a few turns to stop if you have a lathe with no brake and no clutch. That is why larger lathes tend to have both a brake and a clutch.

Martin C

We once had Harry Seacombe filming something (I think it was Songs of Praise) in our department at work and some years later someone else but I can't remember who or what for. What we did is separate off the work area with suitable barriers, made it a non-working area for the period required. We wrote short term risk assessments for what was being done. It meant things like safety footwear or safety glasses which were normally mandatory were not required in the area but equipment brought in still had to be PAT certified where applicable or COSHH assessed if required.

Martin C

I have not read the patent beyond what is in the image above but I think the idea is to produce a movement 1/15000" per revolution of a knob or shaft which is equivalent to a very fine pitch screw but is not a physical very fine pitch screw. Easily achieved with differential pitches.

Martin C