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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: Piston ring grooves
17/01/2022 08:12:11

Are there two rings in one groove? If so then it sounds reasonable. Remember the rings need to be able to move in the groove to spring in and out when temperatures change or to accommodate slight variations in the cylinder bore.

Martin C

Thread: Are standard "M4" nuts & bolts normally fine or course pitch?
14/01/2022 21:09:16

It's the yellow and black one in the first image that is being referred to. I have two, the latest has some CNC codes instead of logs and antilogs. Neither of them has the addition of Roebuck on the front of them, the name of Buck and Hickman's own brand tooling. One is copyright 1980 and the other is copyright 1995. The information in them doesn't go out of date but clearly the use of logs is considered obsolete since people have calculators as stand alone equipment, on mobile phones or pads, or on some DRO units or shop based computers. I think I need to see what is in the latest books to see if a new one is in order, a birthday of Christmas present maybe.

Martin C

PS Just had a look on line for the latest version and I have to say there are some people looking to make a lot of money from selling these at a very inflated price. If you look to buy one make sure it's not overpriced, compare it to other suppliers. As a guide the current prices from RDG and RUBIX, the people who are now the name for Buck and Hickman, should be used as a guide to a reasonable price.

Edited By Martin Connelly on 14/01/2022 21:25:02

Thread: That Strange Calculator Again
14/01/2022 16:06:15

I think most of the little black dots are rivets. 24 around the outside, a circular pattern of 10 around the outside of the circular parts. Can't tell if the others are holes or rivets but I suspect there is one underneath the latch that makes a pattern of 4 on the outer ring.

It may be something to do with coal deliveries. In my youth the coalman came round with a lot of loose coal and a lot of sacks. Most sacks were already filled with 1cwt but if you wanted a smaller amount it would be weighed out on a balance scale. If the coal was paid for by the ton this could help with costs and also this may be something to help work out which weights should be used on the balance scale to get fractions of a cwt in a sack with a minimum number of weights.

Martin C

Thread: Are standard "M4" nuts & bolts normally fine or course pitch?
12/01/2022 23:46:29

Use a cocktail stick or similar piece of wood that can be put into the nuts to get an imprint of the thread and measure what you have got. The last part is a but tricky but should give some idea of the pitch.

Martin C

Thread: Fixing a Magnetic Drill Base?
12/01/2022 16:06:08

I had a look at some data from new mag base drills (Hougen, quoting 115v for USA) and they had a system current 1 amp over the motor current. As indicator lights are likely low power this gives slightly less than 1/2A per coil so I would expect a reactance of of about 230 ohms and a DC resistance below this. If you can find similar data for the one you have it may help figure out if the resistance you have measured is a properly representative value for a good coil.

Martin C

12/01/2022 15:21:06

There could easily be a poor connection or a damaged piece of wire in the circuit that is giving a higher resistance than expected. Since one coil had failed there is a possibility the second is on its way out as well. Since you are considering digging one out you will be able to find what the existing size is from the dead coil.

Martin C

PS Found this YouTube video

Repairing a Hougen mag drill electromagnet


Edited By Martin Connelly on 12/01/2022 15:36:24

Thread: Full size model of some experimental apparatus
11/01/2022 13:55:08

I have seen that video recently as you suspected. I don't know if my daughter has seen it, she is trying to rely on original sources of data and has even gone so far as to translating the German texts herself to avoid any issues with interpretation of what was written.

Ohm was using lines as a unit of measurement, there were a certain number of lines to an inch but I had to point out to her that she then needed to know what inch he was using in 1826 Germany (which wasn't Germany at the time). It's been an interesting process assisting in this task. I have been helping her with the whys and hows of the manufacturing process, and what was possible then compared with what is possible now, so that it may be possible for the reasons for how the design was the way it was may be explained.

One thing we have not been able to get hold of is gold lahn, used to suspend the magnet. There are plenty of people selling gold lahn on the internet but nowadays it is all plastic covered aluminium and real genuine 24 carat gold lahn seems to be unavailable. We have had to replace the fine ribbon of gold he used with a braided polyester ribbon as even the fine hairsprings used in watches have too much torsional resistance to overcome.

Martin C

10/01/2022 16:36:12

Andrew D got there when I was posting. It was Georg Ohm's experiment that he used to derive Ohm's law in 1826.

He was not a trained scientist and kept poor notes. On top of that the original equipment is lost. The PhD is investigating how he used the apparatus, how hard it was to get repeatable results and if the maths he used can result in Ohm's Law as he seemed to make a few leaps in the numbers. Then there is the process he went through to come up with the apparatus as it was not the first he used, he had tried batteries and just one thermocouple before and the apparatus possibly used some parts of previous pieces from those experiments. 

Martin C

Edited By Martin Connelly on 10/01/2022 16:41:58

10/01/2022 16:35:15

Dave you've got the process down pat, the metals in the thermocouple are copper and bismuth. The magnet is aligned along the magnetic north-south when at rest over the zero on the scale (the whole apparatus has to be aligned to do this). When the circuit is made a current flows and the needle is deflected by the resultant magnetic field. The top is then rotated to bring the needle back to zero and the rotation measured against the upper scale indicated the current that deflected the needle.

The thermocouple was used as batteries of the time were not able to give a consistently even voltage and current for the fine measurements needed.

So what happens when different lengths of wire or different thicknesses of wire are used to complete the circuit? That should give away the law named after the original experimenter.

Martin C

10/01/2022 16:22:46

No, not Fleming. It is from around the same time as Fleming and Faraday who followed on from others such as Coulomb and Oersted. To some extent it was based on the apparatus Coulomb used for his investigations into static electricity.

Martin C

Thread: Just Finished, I think!
10/01/2022 16:19:27

Lovely work, though it did take me a few seconds to realize that there was a mirror behind it and it was on its side blush

Martin C

Thread: Full size model of some experimental apparatus
10/01/2022 16:11:20

The needle is a magnet.

Martin C

10/01/2022 15:44:33

The two little cups are for mercury, there were no standards for electrical equipment or common methods of making a good contact. Copper wire was dipped in the mercury to complete a circuit for the experiment. The copper pots are for iced water and boiling water, the silvery bar is bismuth for thermocouple effect but no bullseyes yet.

Martin C

10/01/2022 14:36:38

My daughter is doing a PhD which includes investigations of the original experiments of someone famous, see if you can work out who.

The only information left from the experiments are the original results, sketches and notes on the apparatus. This is my reproduction based on the notes and the sketches shown below.


2022-01-10 14_26_03 experimental apparatus.jpg

2022-01-10 14_27_00 experimental apparatus.jpg

Martin C

Edited By Martin Connelly on 10/01/2022 14:36:53

Thread: Slowing lathe RPM
10/01/2022 10:02:00

435rpm is good for aluminium being cut with HSS at anything up to Ø110mm, you would only need to go slower for a larger diameter or another material. I think Andrew is correct, you need a new expert.

There are plenty of feed and speed tables and calculators you can use, it would be a good idea to use one of these and learn from what has already be found by others rather than muddle along, trying and failing and not knowing what is going wrong. A feed and speed calculator will allow you to eliminate one thing from your machining process so if you still have problems it is one less thing to think about.

If you look at the top of this page there is a black bar with a link labelled workshop on it. Hover over this and you will see processes. Follow this and you will find amongst them a link to a section on feeds and speeds that would be a good place to look at what has been discussed before on this subject.

Martin C

PS. When an RPM is given for a milling tool it can also be used for a workpiece in a lathe. The rpm figures for a Ø50 milling tool are the same as the RPM figures for a lathe workpiece. So an rpm given for a Ø50 HSS tool cutting aluminium in a milling process is the same as the rpm for a HSS lathe tool cutting a Ø50 aluminium workpiece in a lathe.

Edited By Martin Connelly on 10/01/2022 10:08:12

Thread: EMCO FB2 side milling issues
09/01/2022 13:25:23

I think when you are cutting along the Y axis the force vectors on the cutter are acting approximately towards or away from the column centre so rotational forces on the head are unlikely to cause any rotational deflection as they are small. When you are doing the cut along the X axis the force vectors are well away from the column centre line so there is more likelyhood of the head and the column twisting under the forces. Even though the movement is small it could be enough to cause issues as it is significant compared to the cutting depth. Personally I have never cut an edge along the X axis because I have never needed to so I don't know if what you have got is typical of these machines.

Martin C

09/01/2022 13:14:42

Andrew, on posts by the OP under his name there is a link stating a number of photos. This will take you to the relevant photos in the forum album.

Martin C

09/01/2022 09:24:23

For me it is rare to get as good a finish when side cutting as face cutting on top of a workpiece. Here are some things that may help.

You are using a 2 flute cutter. Another thread regarding slot cutting has the mention by Jason that he always uses 3 flute cutters. These are a better option than 2 flute because they are stiffer. A 2 flute cutter can be looked at like a twisted ribbon, even carbide 2 flute cutters are not as stiff as 3 flute cutters.

I think there may be too much play in the gibs and when you are unlocking an axis it becomes too loose, try pinching the moving axis slightly so there is some drag and see if that improves things.

I would not rely on just two clamps holding that vice to the bed like that, I would use four because a heavy cut may grab the workpiece and twist the vice if there are no tenons locking it into the slots.

Try a larger diameter 3 flute HSS cutter with a polished finish, coated cutters are no good for aluminium alloys, the coating just encourage the aluminium to stick to the cutting edge and give a poor result. See if you get a change in the finish from a faster or a slower speed or feed, sometimes the cut just hits a resonant frequency of the machine and a different number of cutting edges or a small change in speed (with a corresponding change in feed rate) may change the frequency and completely change the resonance of the machine, these mills are only small even at 300kg compared to an industrial machine. This makes them more prone to resonance and vibration. Make sure it is always cutting and not rubbing, this will show up as a constant flow of evenly sized chips coming off the cutter.

Martin C

Ps Get a ball bearing nut for the ER collet chuck if possible. They allow a far greater clamping force on the tool with the same applied torque, there is a possibility that the collet is not closed down tightly enough.

Edited By Martin Connelly on 09/01/2022 09:27:49

Thread: Collet Choice
06/01/2022 16:17:37

Some thoughts.

I have not used morse taper collets but they have a bad press regarding removing them from some types of machine. Ideally if you use morse taper tooling you would want either a slot to allow use of a taper drift or a drawbar that was able to eject the morse taper from the spindle. The bad press is that without the mechanisms for easy removal they can be overtightened in the socket by too much drawbar tension and then they require a lot of effort to remove.

They do allow for more space under the spindle than an ER chuck and may be cheaper if you only use a small number of cutter shank diameters.

If you get a morse taper ER collet chuck it would be easy to put it in the spindle and leave it there then some point in the future find it is very hard to remove as it has not been disturbed for some time.

There is nothing to stop you from using ER32 for most work and having a few morse taper collets in common sizes for when you want a bit move space under the spindle.

Large diameter cutters or fly cutters can have a lot of reaction force on them. The shorter stick out when used with a morse taper collet would probably be better than the longer stick out that would result from using an ER collet. The more rigid a set up the better when making swarf. So if sweeping a large surface with a fly cutter is likely use a morse taper collet, using a Ø5 milling cutter in a morse collet may be hard to see if the spindle nose is over the workpiece.

Martin C

Thread: Controlled release of a Clarke Bottle Jack fitted to an engine building stand
06/01/2022 15:02:35

Dave, how far down can it go before it hits the jack? How long a screw can you put on it? It's a concept drawing not a scale drawing. As I said earlier you can put the operating knob in a convenient position or even make it so you can use the supplied handle from outside the danger area to operate it. What about a flexible drive shaft to turn the screw, lots of options.

Martin C

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