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Member postings for Martin Connelly

Here is a list of all the postings Martin Connelly has made in our forums. Click on a thread name to jump to the thread.

Thread: Old School Drawing Exercises and 2D CAD
03/07/2020 14:36:37

To me it looks like the curve produced by rotating a circle 45 degrees in two planes. At 1.5 radius this would produce an oval 3 high 2.12 wide. Rotate this 45 degrees anticlockwise to produce the example given.

Martin C

Thread: micro switch
02/07/2020 17:53:07

You can buy small long lever microswitches that I think would replace these if the lever was bent to suit.

Martin C

RS part 0150710 for example 

Edited By Martin Connelly on 02/07/2020 17:59:43

Thread: My new lathe a Warco 918
02/07/2020 15:16:20

Dave, you are correct, the original circuit works as drawn. It does require start up current to flow through the diodes though so heavy duty diodes would be required. I wonder what would be specified. Don't think my version needs manual resets. I've drawn the switches open in the operated position when they should be closed (nc contact) which may be why you think it needs resetting. 

Martin C

Edited By Martin Connelly on 02/07/2020 15:22:03

02/07/2020 13:15:59

Thinking about the diodes for the circuit I drew, put positive on terminal 1, negative on terminal 2 then the diodes should be as follows:

The top switch should have the triangle pointing to the left, bar on the left.

The bottom switch should have the triangle pointing to the right, bar on the right.

If the motor runs in reverse to what you expect reverse the motor connections as it is easier than having to swap the diodes around if you change the input to the switch.

The bar on the diode symbol matches the band found on most diodes.

Martin C

02/07/2020 12:59:08

I edited the previous post as you replied so I will repeat what I put in in case you missed it. The diodes on the first diagram are the wrong way round.

Martin C

02/07/2020 12:44:07

The diodes will be for spark suppression, I was too lazy to draw them in the quick pencil sketch. The chances are your switch terminals will be the two in the middle of each side are the equivalent of 1 and 2 in the sketch. One end of the switch will be the a terminals and the other end the b terminals. A multi-meter or continuity checker (battery and lamp/led) would soon verify this. I would expect three on one side will be 1a,1, 1b and the three on the other will be 2a, 2, 2b if the switch was marked like the diagram.

Martin C

By the way the diodes shown in the original diagram are the wrong way round and would bypass the switch if you had positive and negative supplied as shown.

Edited By Martin Connelly on 02/07/2020 12:57:48

Thread: Old School Drawing Exercises and 2D CAD
02/07/2020 10:58:43

We had a drawing of a pipe at work, done by a professional draughtsman with years of experience, that I had to point out was impossible to make. He said if we can draw it you can make it. What he had drawn was the equivalent of a Penrose triangle. If he had 3D CAD it would have been obvious but he was doing it 2D. I learnt to use AutoCad when it was 2D from the supplied paper manual that had a very good tutorial to work through. I was also lucky enough to be doing it at work so effectively was paid to learn it. Going to 3D was not hard as I spent a lot of time at work checking drawings for production before they were issued. You learn to turn 2D images into your own internal 3D model as a result.

The triangle problem is simple, learnt that in maths at school. Bisect one of the base angles and project the line to the centre line. Estimate by eye gives 7, trig gives 7.2 if I remember yesterday's result correctly.

Martin C

Thread: My new lathe a Warco 918
02/07/2020 10:22:57

The circuit you want is to have 1a and 2b connected to one motor terminal, 1b to one limit switch and 2a to the other limit switch. The remaining two limit switch terminals connected together go to the other motor connection.

Martin C


Sketch added

Edited By Martin Connelly on 02/07/2020 10:28:53

Thread: Mill unexpectedly cutting crooked
01/07/2020 11:53:20

It does not seemed to have been mentioned yet but does it make difference if the spindle is clamped tight or if it is a bit loose?

Martin C

29/06/2020 21:01:33

Use a 16mm or 20mm cutter. They are a lot stiffer than 12mm cutters. That will rule out the cutter deflecting. Keep small diameters for when you need a small diameter.

Martin C

Thread: The fit of tapers
29/06/2020 18:05:24

The couplings went up to 28000psi, the pressure to fit the hub was about 20000psi. There had to be a bit left above fitting pressure in order to remove them when necessary.

Martin C

Edited By Martin Connelly on 29/06/2020 18:06:01

29/06/2020 15:16:30

Found a photo of a hub similar to the one above being fitted or removed.

hub fitting.jpg

Martin C

Edited By Martin Connelly on 29/06/2020 15:20:33

29/06/2020 14:43:19

I have designed tooling for fitting items as described by Nick. The drive shaft hub in the tooling is about 250mm diameter for an idea of scale.

hub fitting tooling.jpg

The light blue is the shaft, the dark blue is the hub and there is a hollow pancake jack (the brown item with a nominal coupling sticking out the side) to push the hub on to the shaft. Pressure was applied to the jack to bed the taper then oil was pumped down the centre of the shaft to oilways on the taper while the pancake jack kept pressure on the hub. We had to measure how far up the shaft the hub moved after bedding in to be sure it was on far enough. We used CEJN couplings to handle the pressures that went up to 28000psi.

When the hub was removed there had to be a restraint system in place as the hub would otherwise shoot off at very high speed.

The bottom right inset has an alignment hub (purple) shown that was fitted to align the machine then removed for the coupling hub to be fitted later. It was made by a company called Bibbys.

The shaft taper was 1:20

Martin C

28/06/2020 09:37:57

The ability if a taper to lock depends on the materials used, the finish on the faces, the taper angle and the presence or absence of any lubricant. The linear position will change if you take some material off the surface of one or both parts. It will also change if there is any bedding in of uneven surfaces. If this is what you are concerned with then the formula is the wear divided by the sine of the half angle. As an example if you machined off 0.1mm or had the equivalent wear and the taper half angle is 15 degrees then the linear movement along the taper will change by 0.1/sin(15) = 0.38mm.

Martin C

Thread: Stuart 10V Build Log - Complete Beginner...
26/06/2020 12:43:04

You want the piston to be a close fit in the bore and the cross head to be a close fit in the standard. The piston rod hole should be close to the piston rod but not rubbing. The packing will hopefully then seal around the piston rod whilst aligning itself to the correct position for the assembly to work correctly.

Martin C

Thread: 2mm endmill help
26/06/2020 12:26:36

The recommended depth of cut was 0.2mm not 2.0mm. Lots of small passes with the correct speeds and feeds and overlap of about 1mm (50%) as a starting point. Make the tool last to the end of the job.

Martin C

Edited By Martin Connelly on 26/06/2020 12:34:04

Thread: Smart and Brown Sabel
25/06/2020 21:07:15

Turn the leadscrew and the dial will turn to wherever you want it to be. Move the carriage along the bed and the dial will turn to wherever you want it to be. There is no datum to line the dial with the datum on the casting. If you are saying there is a mismatch between a point on the dial and the datum when the half nuts are engaged then the answer is it doesn't really matter as long as you know what the error is.


Edited By Martin Connelly on 25/06/2020 21:11:11

Thread: Need to know about iPad 'air'
25/06/2020 21:02:51

I have had Zoom meetings with my daughter with me using a Windows 10 laptop and her using an Apple computer. So I can confidently say that Zoom is platform independent. Use anything for the meeting.

Martin C

Edited By Martin Connelly on 25/06/2020 21:03:13

Thread: Mamod safety valve
25/06/2020 16:15:07

Force is pressure times area. If you had 10psi and an area of 0.1 square inches you would need a spring applying 1lb of force. This 1lb would be from an initial compression so you need to know the spring rate, the relaxed length and the assembled length. The area is probably the inside area of the rubber o ring's hole. I think the likely area is a lot less than 0.1 so a spring applying a lot less than 1lb will be required.

Martin C

Thread: 2mm endmill help
25/06/2020 09:05:38

Here's the calculation for your chip load (advance of the tool per pass of the cutter tooth).

Chip load is travel speed/flutes x rpm. Taking the possible top speed of 15000rpm and travel speed of 50mm/minute and assuming a 3 flute cutter that gives 50/(3 x 15000) = 0.00125mm per tooth per pass. That is definitely rubbing territory. Let's go for 10000rpm and 2 flutes and you get 0.0025mm per tooth per pass. Still in rubbing territory.

So babying the feed but too aggressive on the depth of cut seems like the summary from previous posts and this calculation.

Does the supplier or manufacturer of the cutter have data for it? It would help avoid breakages. If not then the Little Machine Shop feeds and speeds calculator would be worth checking out.

Martin C

Little Machine Shop calculator

Link added


Edited By Martin Connelly on 25/06/2020 09:08:29

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