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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: bending small bore copper pipe
10/11/2017 17:05:49

img_20171110_165519.jpgimg_20171110_165500.jpgPhotos of the cardboard computer I have for selecting CNC pipe bending machine tooling.


Martin C

10/11/2017 13:59:54

There are rules for the tooling needed for CNC draw benders that allow selection of necessary tooling. The larger the OD to wall thickness ratio the more likely you are to need support inside the tube. Also the tighter the centre line bend radius is to the OD the more likely internal support will be needed. I have a cardboard computer (think slide rule made of cardboard) for this purpose. You find factor 1 which is wall thickness to outside diameter figure. Then factor 2 which is the centre line bend radius to OD. On the reverse side you set the slide to the factor 1 position and look down against a window to see what is against factor 2. This tells you if you need a wiper die, plug or ball mandrel and if a ball mandrel is required how many balls.

For example 3/4" 16swg tube has a factor 1 of 15 (they are coarse figures for the factors). With a bend radius of 3D (2.25" the factor 2 value is 3. The result is the table says this bend needs a plug mandrel but no wiper die. Reduce the bend radius to 3/4" and it says a one ball mandrel with wiper die.

This works for stainless steel but I don't know how applicable it is for copper tube, the bending tool selector does not say anything about material.

Martin C

Thread: Rotary table problem.
09/11/2017 14:23:52

My 4 jaw independent chuck is significantly thinner than my self centering 3 jaw chuck. Might be a future option if the needed space is not too much more than you have now. Otherwise collets straight into the mill spindle as stated earlier is a possible solution if you can do it.

If you have a DRO then fit the plate on the machine and drill holes using coordinates (Zeus book has details) or built in bolt hole circle function on the DRO controller.

Martin C

Thread: Pro's and con's with a small verticle mill
08/11/2017 10:34:34

The large x axis travel may sound like a good feature on this type of mill but what you should realize with this design is that the support for the bed is quite narrow. The centre of mass of the bed and anything on it can be beyond the support.This means that for normal operation the gibs need to be loose enough to allow easy movement and as a result may not be able to keep the bed from tilting at the extremes of travel. The weight of the bed and whatever is mounted on it can cause it to sag where it is unsupported. Adding a power feed will contribute further to this problem. It does not matter too much for short items as they move the centre of mass towards the support but for something that requires the full travel it may result in a surface that is less flat than you expect.

Martin C

Thread: About tap & die's
05/11/2017 12:58:46

Zeus books are still available from Buck and Hickman and probably other sources.

Martin C

Thread: Spurious Accuracy
03/11/2017 19:00:54

And who amongst us has a workshop with temperature controlled to the same standard as a calibration lab and can leave everything for three days to achieve the correct temperature for accurate measurements.

Martin C

Thread: How do you ensure the milling head is parallel with the table?
03/11/2017 09:16:21

If the need is to rotate the ram assembly in the xy plane then clamp a suitably sized engineers square (in good condition of course) to the table. Move the table along the x axis to set the square correctly. Then with the indicator on the ram move the ram along the y axis and adjust the rotation of the ram assembly in the xy plane until the indicator shows the ram is running parallel to the y axis.

Martin C

Thread: 3 phase inverter query?
31/10/2017 10:42:46

Modern invertors monitor the current in the phases to apply feedback to the control electronics. Running two motors in parallel which may run at different speeds due to varying loading may confuse the feedback circuits. I would not try it unless the manufacturer says it is ok to run like that. You may just keep getting false fault reports that shut down the invertor at the worst possible time (is there a good time?).

Martin C

Thread: Bandsaws and their blades
26/10/2017 18:56:27

They are probably conversions from a feet and inches value (5' 4.5" with varying levels of rounding. The adjustment for the lengths in your post only requires 3.5mm of adjustment. There is usually a lot more than this in order to allow the wheels to get close together to allow easy blade replacement. I think I would assume that they all take the same blades and will have enough adjustment to cope with the natural variation that will present on replacement blades.

If you go to someone like Starrett they make the blades to order from a long length. You tell them the blade specification you want and how long and they cut it off and weld the joint. There are so many different blade lengths required that they would not want to have them in stock just in case someone orders one. They could end up with a lot of rusty blades that need to be scrapped off.

Martin C

Thread: Electric chain hoists/carriages
19/10/2017 14:08:51

What about a chain operated carriage llke this?


Martin C

18/10/2017 19:25:43

250kg single phase in 110v or 230v available here


Martin C

Thread: Convensional vs climb milling
15/10/2017 10:20:55

C J, cut out about 59mm diameter first then clean up the edge to 60mm diameter. To finish to size turn the plate anticlockwise viewed from above to cut conventionally for the reasons given by Paul earlier. When the centre is close to coming free take care as it can be flicked into the tool or out towards your hand.

Martin C

Edited By Martin Connelly on 15/10/2017 10:21:35

Thread: What is it?
15/10/2017 09:25:14

Maybe a parallel pin pusher for removing or refitting them without banging a parallel pin punch against the pin.

Martin C

Thread: Looking for an MT2 Milling Chuck.
30/09/2017 18:25:58

I have never had a drill slip in an ER collet, 3 jaw drill chucks are a different matter.

Martin C

Thread: Making a knuckle joint.
30/09/2017 18:17:26

EDM would do it. Would need someone else to do it for you probably. Another option is to make a sandwich with a pre-machined central plate.

Martin C

Thread: diy dovetail cutters
25/09/2017 13:01:00

There is a recent thread on this.


Martin C

Thread: Chuck a mile out
24/09/2017 13:44:48

If you want accuracy then don't use a self centering chuck, use a chuck with independent jaws that allow you to set up work accurately. You can use the scroll chuck to turn all the features that can be done in one setup and they will all be concentric. Once the workpiece has been removed from the chuck it needs to be set up in an independent chuck or accurate collets to continue This topic comes up regularly.

Martin C

Thread: Power feed drilling
17/09/2017 16:32:48

I power feed on my CNC using manual data input (MDI). I set the drill to the correct rpm for the size of drill and feed at 30mm/min. I drive straight through for holes up to 3 times diameter. I only peck beyond this.

Martin C

Thread: Oval S/S tube required
03/09/2017 17:39:16

Yes, seamless.

Martin C

Thread: Machining Tungsten
03/09/2017 09:03:06

Do you know anyone who could try thread milling this material? I suspect that would be the way it would be done in an industrial production process.

Martin C

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