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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: Shimming Techniques
24/01/2021 10:16:43

If at first you don't succeed.. don't try skydiving!

My experience with backlash in the X and Y axes was that there was quite a lot in the lead screw to table connection. The leadscrew nut had some wear compensation with a split nut but there was none around the handwheel area. The parts were held together with spring pins through the handwheels into the leadscrew shaft. It may be a good idea to put your DTI on the table and indicate on the end of the leadscrew. See what reading you get from reversing the direction of table travel.

If you have a DRO backlash in X and Y is less problematic but backlash can still reduce ridgidity of the system if you do not have the movements locked down. Climb milling is something some people recommend against because of the issues with the cutter driving the table in a direction that is free space due to backlash. Get rid of backlash and you do not have this worry.

Martin C

Thread: The bomb in the workshop
24/01/2021 09:35:06

I fitted a timed relay operated vent to the base of a large receiver once. It opened once a day for about 5 seconds to release any water and was to avoid someone having to remember go out and do it manually. Even that operating if you were not expecting it would make you jump, and that's with a sintered exhaust muffler on it.

I don't think his idea of cooling the air going into the tank would help, it is not removing the water content from the air. Hot air will hold more moisture but cooling it down does not remove it in a closed pipe.

Looking at his tank it has a large plugged boss with the drain at the centre, I would think that is for internal inspection and is probably of more use than tapping it to see if it is weak at any point. I suspect that the weld was a stress raiser and that repeated pressure and release cycles had flexed it. The requirements for weld caps to avoid stress raisers are quite clear, more weld is not a better weld and sharp transitions are a no-no. Corrosion may have contributed but without proper examination of the exposed surface where the failure originated it is impossible to be sure what the root cause was.

Martin C

Thread: Motor reverse switch 3 phase
24/01/2021 09:01:26

You are close to correct but not all the way there. Connect L1 and link to 1 and 3, connect and link L2 to 5 and 7, connect and link L3 to 9 and 11.

Connect and link A to 2 and 4, connect and link B to 6 and 12, connect and link C to 8 and 10.

Check this out on a bench first with a meter or continuity tester first to be sure it works as expected. Make up the link wires (6 off) to join the terminals 1-3, 5-7, 9-11, 2-4, 6-12, 8-10,

In position one note what L1, L2 and L3 connect to, and check for continuity or not between the L1, L2 and L3 positions. I would expect them to connect to A (2), B(6), C(10) respectively and no continuity between them.

In position two repeat as above, I would expect them to connect to A(2), C(8), B(12) respectively and once again no continuity between them.

In position 0 I would expect no continuity between any terminals except where linked.

Note this system is for use with a 3 phase supply that is not being fed by a VFD as stated above. They don't like switching the terminals when on.

Martin C

PS this is with the advantage of the table, up to then there was some guess work going on so it is important to have full information before going ahead with this sort of wiring.

Edited By Martin Connelly on 24/01/2021 09:08:27

Thread: Smart & Brown model A drawings
23/01/2021 09:22:11

You need to go to Join ( to register.

The group is called SmartAndBrownLathes

Martin C

Thread: Motor reverse switch 3 phase
23/01/2021 09:10:54

The usual way 3 phase motors are reversed is to swap two of the phases feeding the motor. Without full details of the switch that is all that can be said for definite. There are probably lots of wiring diagrams for dedicated switches but since the dedicated switches will be likely be just 2 or 3 positions (forward/reverse or forward/off/reverse) they will not help. Can you confirm if the switch is 12 positions and not 12 connections. 12 position rotary switches are available but would usually not be suited to switching motor wiring.

Martin C

Thread: How not to use a clamp
22/01/2021 15:20:06

Oldiron, I said machining forces not milling forces.

Any setup where the clamp can rotate the step block without the clamp being raised is a poor setup. By clamping on the steps further down the step block any rotation about the heel of the step block will try to push the clamp upwards, this is resisted by the clamp bolt. The top lip is not a good place to use on its own to support the clamp because it minimises this lifting of the clamp. The operation in the video was not brought up because in the end it is irrelevant, the point is this is an example of poor clamping practice that should always be avoided so that it is not used in machining where larger loads are applied to the workpiece.

I think we should always promote best practice.

Martin C

22/01/2021 10:23:43

I found this example of someone showing how to use a mill for a model engine and thought this poor clamping practice needed highlighting for any beginners who may think it is acceptable.


The clamp is resting on the very top lip of the stepped block, the applied force is down and slightly outward due to the angle of the clamp. This is because good practice is to have the supported end of the clamp higher than the nose that is on the workpiece. The direction of the force vector is therefore both down and away from the clamped part. If you project this force vector it will be at the edge of the stepped block where it is chamfered and must be very close to being just past the support at which point everything will fall over.

Now imagine a small additional force from the machining operation pushing this force vector beyond the support, the result is a failure of the clamping setup when machining. Not a good outcome.

Better practice would be to put another smaller step block on the one being used and rest on that or to raise the step block on some other material so that the end of the clamp can engage with the steps much like the one to the left is being used.

Martin C

Thread: Vertex (V4?) Rotary Table
22/01/2021 08:35:46

Nick, I have got 2 A levels in maths and an engineering degree and I got lost at the first line, 19 x 4d = 342d

Martin C

Thread: Smart & Brown model A drawings
21/01/2021 22:50:35

Just to let interested parties know, I have added Smart & Brown Model A manuals, specifications and parts list to the Smart & Brown group files.

Martin C

Thread: Vertex (V4?) Rotary Table
21/01/2021 22:44:35

Nick, use a calculator with a D°M'S button, it's much easier. 360/19 = 18.94736842 press D°M'S and get 18°56'50.53

Or if you do not have this function on a button (some numbers are rounded):

18.94736842 - 18 = 0.94736842 note 18 is degrees

0.94736842 x 60 = 56.8421 note 56 is minutes

56.8421 - 56 = 0.8421

0.8421 * 60 = 50.5263 note this is seconds

so 18° 56' and 50.5263"

Martin C

Thread: Fusion 360, Mach4 and first test of cnc router
20/01/2021 15:33:25

Geoff, Mach3 has Z inhibit burried under Config, Ports and Pins, Mill Options. I have a toggle and DRO on the Program Run screen but I don't know if it is something I added to the screen because it is hard to find.

Martin C

Thread: Advice for surface finishing
20/01/2021 08:50:03

I have bought them from JB Cutting Tools. I came across them because other people on this forum said they used JB and were happy with their offerings.

Martin C

PS I would just add that when you get inserts in boxes of ten as opposed to singles often they have a chart on the back of the box detailing their recommended depths of cut, feeds and speeds for various materials. It is probably worth looking at these for whatever you get and try to work with them. Also RPM is often a maximum not a recommended value.

Edited By Martin Connelly on 20/01/2021 08:58:06

Thread: Fusion 360, Mach4 and first test of cnc router
19/01/2021 19:15:41

Rolling around corners also keeps the cutter engaged with the workpiece. Usually a better option. The facing wizards in Mach3 do not have this option (that I could find) so I had to write a parameterized file to do it for when I wanted to do it without going down the CAD CAM route.

Martin C

Thread: Pressure Gauge feed
18/01/2021 13:16:17

The measured pressure can be affected by the flow of fluid (gas or liquid) past the tapping point. It may be this that was being referred to. You need a tapping point where there is either no flow or constant flow past it to avoid this issue. Without knowing the system you are looking at I don't know if this is a valid reason to consider.

Martin C

Thread: Advice on best approach to milling recess in end bar
18/01/2021 09:46:49

2021-01-18 09_38_50-new xp with autocad 2010 on desktop-qessl6m - virtual machine connection.jpg

Setup as shown with cutter in position A. Move table to give position B then back to A. Repeat for the other two cut outs. Change offset to the second diagram, move to position B then rotate the table to meet first cut. Remove the remaining material towards the edge. Repeat for the other two cut outs. If you want to remove the fillets completely you could run a small cutter down them to give an undercut.

Martin C

18/01/2021 09:12:22

You need to decide what is acceptable in regards to fillet size and where they will be. The part can be approached axially or radially or both.

If you do it axially you will need align the RT to the spindle then offset either the x axis or the y axis half the milling cutter diameter to do one side of a cut out, do all three edges first. Offset the RT the opposite way to do the other edge and with that offset rotate the table round to meet the first cut. Then machine away any remaining material towards the edge.

I would make a paper or card cut out of the required part and stick it to the top as a guide to make sure you were going in the correct directions as you go.

I'll knock out a diagram.


Thread: Etching brass
16/01/2021 09:25:09

George B, I always remember the cathode in cathode ray tubes spit out negatively charged electrons so must be negative.

Martin C

Thread: Thread Cutting Gears on Seig / Axminster SC2
16/01/2021 09:18:33

I think this is similar to the Grizzly g9866 lathe. Their manual is quite clear so have a look at pages 26 and 27.

Martin C

Thread: Etching brass
15/01/2021 17:32:41

Coincidentally I was looking at this YouTube video today. The "bonus material" at the end may be of some interest to you.

Martin C

Thread: Socket/thread sizes
14/01/2021 16:42:13

DC31k, Gedore have a series of sockets designated by them as D19. In that series D19 29 is a 29mm AF socket. What do you want explaining? I think the original post has some numbers from different sockets mixed up or the sockets have been marked by someone other than Gedore and they have made mistakes.

Martin C

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