Member postings for Martin Connelly

Photos are inserted where the cursor is when the camera icon is selected. Just make sure the cursor is in the correct place each time you want to insert a picture. I usually press the return key a few (3) times to make spaces between two sections of text and photos then position the cursor between the two sections of text where I want the photo. This also ensures text starts on a new line not to the right of the picture. Often I do all the text first and add photos last.

Martin C

The only notable aircraft I have seen in the past few weeks is a powered glider. I think it was the same one on two different days but it could have been two just coincidently passing the same point a few days apart.

Martin C

There is a thing called the safety triangle. This says something like for every 300 - 600 near misses (unsafe act) there will be 30 cases of damage, 3 injuries and one case of major damage. These examples you give are the base of the triangle, the 300 - 600 near misses. if someone does this sort of thing 600 times the chances are high that they will have done some damage, injured themselves a few times and are looking at a case of major damage soon.

There are plenty of variations on the safety triangle so you take your pick on the number of levels and numbers put in each level but they all follow the same pattern.

Best thing to do is keep the near misses as close to zero as you can by avoiding the unsafe acts.

Martin C

I have never liked digital callipers. I always find that they give inconsistent readings for me. Change where the pressure on the jaws is, change how much pressure you apply with the thumb wheel, accidently reset the zero and not notice. Too many ways for them to give odd readings. Never have that problem with my vernier callipers with thumb wheel screw adjustment and they are always within tolerance when cross checked with a micrometer or with gauge blocks.

Martin C

You can always stick a square collet block into a 4 jaw chuck and dial in the required concentricity. Arc Eurotrade sell all sizes with and without nuts and all have a through hole. I would make a setting bar with an accurate centre drilled in one end to ensure the positioning of the block is along the spindle axis.

Martin C

Paul, sorry but I am going for the pedant role here

Tubes for manometers are not always U shaped. I went to a museum at Farnborough where they had test equipment used in the investigations into flight and the design of aerofoils. Their manometers were V shaped with one leg vertical and the other sloping at about 30° from the horizontal in order to make the difference in levels more readable.

Additionally at work we hade low pressure differential transmitters by Rosemount that were referred to as manometers even though there was no tube of any shape containing liquid.

Martin C

The scrap bins in the raw material stores where I worked always had some cut off ends of bar stock in them. They were cut off and discarded due to the inclusions in them. As the stock is cold formed the ends curl over towards the centre and in the worst cases some of the rubbish on the end face ends up being squeezed into the material where it is hidden. These discarded ends were usually in the region of 100mm long to be on the safe side. A stockist who is cutting off parts and sending them to a customer does not want the cost of too much waste so would probably cut off the minimum to remove the curled over end and no more. The result is if you get the first piece cut off a length of stock there is a risk of the end face scale and corrosion being embedded in the material to a significant depth.

Martin C

Nigel mentioned reversals. Is he doing the two steps forward one step back manual rotation of the chuck type of operation? Feel is very important for these small threads in soft material. If he is trying to cut the full thread under power then power back out without clearing chips then he will find it can strip threads very rapidly.

Martin C

I said earlier 16 bit when I should have said 32 bit. I believe some 64 bit computers will not run Mach3

Martin C

Edited By Martin Connelly on 08/08/2023 19:39:08

Regarding grinding chuck jaws, When I got a new set of inside jaws for one of my chucks the runout was noticeable. I just opened them up to about 60% of the bore of the chuck and then gripped some steel spacers with the 120°sides. I then marked the gripping faces of the jaws with a marker pen and used a very stout boring bar with a carbide tip to clean off the marker pen. A light stoning finished it the job. Grinding was popular before carbide was available but is not necessary nowadays. I think I used a polished and ground carbide tip.

Martin C

As long as you have 16bit computers that will run XP or Win10 and have a USB port I don't think Mach3 is going to disappear very fast. It has been around long enough to be stable and a lot of people are using it without problems. I know there are some people who would like to improve threading due to the single pulse per rev causing issues on low power lightweight machines, but if you have back gear, a drive train with plenty of mass and a sufficiently powerful motor there is no problem. I think people who converted machines with a speed control that reduced motor power were the ones having the biggest headache with threading.

Martin C

Soft jaws have the advantage that you can also machine a back stop in the jaw so that if there is a machined lip on the part you are working on it can be repeatedly replaced the same depth into the chuck as well.

Grinding the jaw faces to hold a hexagonal part may not give the accuracy you are expecting because the 120° faces of the jaws may not be accurately machined and also you will have a sharp edge to the ground faces which will damage the faces of the hex part or in turn be damaged by the hex.

Martin C

I am sure if members of this forum chatted to potential prize winners of a handicraft competition we would be asking about methods of manufacture, about anything that was difficult to do and what tools were used. Surely potential judges could ask similar questions to a short list of top entries and present prizes based not just on the entry but also on the work put into the item. Make an event of it like a lot of the programmes on TV where presenters go around and talk to people who are painting, sewing or cooking. This fuller picture of the entry and the entrant would enable prizes to be awarded based on more than just presentation of an object.

Martin C

For the purposes of threading what the tumbler gears do is effectively make it easy to add an extra idler gear in to the gear train then revert to normal RH threading afterwards. Unless you are going to be doing a lot of LH threading then reverting to RH a modification that allows you to add an idler gear into the gear train, when the odd occasion requires it, would be a simple solution. If you are planning to do a lot of feeding outwards when facing or towards the tailstock when surfacing this may be all that is required.

Martin C

Joe Pie did a video on the idea that a single point thread cutting tool does not need the correct angle on the second face. Worth a look.

Martin C

Roger, since you have an ape as your avatar maybe you should be aware that a mandrill is a primate and what you have snapped is mandrel. Snapping the end off a mandrill makes a different type of mess

Martin C

I think the point of running the saw down each side as mentioned in Jason's post of 10/7 (the one with a video) is to reduce this curl. I also think you need a very evenly sharpened slitting saw blade with no uneven wear on any of the cutting tips. Such wear will create forces that push the blade off line with the potential result of the part curling. Did you use a new blade or one that has already been used for another job? I also suspect that a thinner blade will induce more curl than a thick one, but this is only a guess based on a thicker blade being more rigid.

Martin C

We cut a lot of stainless pipe where I used to work and the go to tool for the larger sizes was a bandsaw. For smaller tubes we used a Pedrazzoli Brown chop saw (two speed, always on low speed) without coolant to avoid contaminating the tube with oils or washing chips into the bore. This meant that the saw blades needed regularly changing because they lost their edge or clogged up with chips in the gullets. We had a pile of used blades and a pile of fresh blades and just changed them over as required. When the pile of used blades was somewhere between 20 and 40 we sent them off for resharpening which also cleared the gullets. Since they only needed minimal sharpening when used like this it was cheaper per blade to get them sharpened in large batches. We had a lot of money invested in all those blades but it was worth it when compared to the cost rate in the department and the potential cost of delays to workflow.

Martin C

Surely there must be some position where the zero is visible and the slots are aligned with at least one axis. At this point add your own fiducial indicator plate where the zero is, as suggested by DC31k

Martin C

If you want the arbor true to the jaw faces (at least at one diameter) then finish machine the arbor when it is screwed into the chuck and with the chuck gripping a machined in place cylindrical part in the lathe (like Dave has the chuck mounted in the photo of 28 July). As it is overhanging you should also put the centre drill into the rear of the arbor with it assembled like this for support when final machining. Use a new drill sleeve for checking the taper you produce without having to remove the assembly from the setup.

Martin C