Member postings for Martin Connelly

if you wire the motors in series you will reduce the voltage across each motor to 25% of the boards output (based on identical motors). Putting them all in parallel will put the board's output voltage on each motor but will increase the output current fourfold over one motor (same caveat). A hybrid of two parallel motors in series with another two in parallel will halve the voltage on the motors and keep the output current the same as a single motor.

So if you have four 12 volt motors in series on a board with a maximum output voltage of 36 volts the motors would be expected to only be supplied with 9 volts. Possibly not what you want.

If you put the 4 motors in parallel then supply them with 12 volts and they all draw 25 amps inrush current then the board, wiring and power supply would have to be able to cope with 100 amps for a short time.

Answering "what is best? " is dependent upon what load the motors will have to overcome, the power supply being used and how much stress you are willing to subject everything to. The stress is related to how close you want to take things up to maximum rating for the system and for how long they would be subject to this stress.

Martin C

Just read you are using two 12 volt batteries. Put in series these will give 24 volts and so two pairs of parallel motors in series will give 12 volts across the motors if the 24 volts is on the output terminals.

Edited By Martin Connelly on 26/07/2023 08:39:24

It may be worth trying a resistor between the high speed side wire and the pot terminal of equal resistance to the pot. If it is only suppling a voltage for speed control this will halve the voltage on the wiper terminal so give slower speeds over the range of the pot. If the useful speed is at position 1 then this would move it to position 2.

Martin C

Just an afterthought, what is the speed that you consider useful? How long does it take the table to move 250mm for example?

Edited By Martin Connelly on 24/07/2023 00:49:21

Mike, you have to have no lactose in your diet for a couple of days to recover from the effects of inadvertently eating some. The other option is to buy some lactase tablets, they are quite cheap, and use them to see if that helps. It saves having to try and find out, in restaurants for example, if there is dairy in a meal and hoping they give you correct information.

Martin C

As it is brass I think I would make it using a slitting saw and CNC on the mill. Finish with a small amount of filing and polishing if needed.

Martin C

My wife has recently become lactose intolerant. Turns out that's quite common as people age. She now uses soy milk or other dairy substitutes for coffee where the actual taste is somewhat disguised, but you can buy decent lactose free cream and importantly lactase tablets to take if you do eat lactose containing food. This is useful because it turns out that not all lactose free foods are 0% lactose and also there are a lot of foods that have milk or milk products listed in their ingredients.

She bought some lactose free cheese that has a slightly odd texture but is not too bad otherwise but cheeses come in many textures so may just be the cheese texture. However she tried doing cheese on toast with it and that resulted in something that failed to resemble cheese on toast.

Taking the lactase tablets before eating means she can eat things she would now have to avoid so that means pizza, or pasta carbonara is still on the menu as are many curries that use dairy in their sauces and anything with butter is risky. The things that she would most miss (I think) are chocolate and cream cakes. She bought some lactose free chocolate and that was no different from ordinary chocolate, except it turns out that if you eat enough (70g) it is not 100% lactose free.

Martin c

A recent survey commented on how many men had no one they could or would really call a close friend, many were happy in their own company and with doing a relatively solo hobby, close to 20%. Maybe this is a sneaky way of double checking that data.

Martin C

Edited By Martin Connelly on 19/07/2023 22:05:51

Hopefully the brass will not slip too much in the drill chuck. If you do find the brass is slipping (since it is a relatively slippery metal) put some paper between the brass and the drill chuck jaws.

Martin C

Since ER32 collets go up to Ø20 it is possible to hold cutters up to this diameter in the tailstock if you have a suitable ER32 collet holder for the tailstock. I use an MT2 to ER32 collet holder in my tailstock for Ø19 shanks on annular (Rotabroach for example) cutters. Probably not worth getting unless you are going to have a regular need for this type of size.

Another option is to mount the cutter in the tool post. How easy this depends on a number of factors we don't know regarding the machinery and tooling you have.

The holding of tools with hard polished shanks in a lathe chuck can be problematic due to the low friction of the shank in the lathe. This will probably not be as big an issue with brass as it would be with working on steel but you are doing quite a large diameter with the ball end milling cutter. It will have a long cutting edge in contact with the brass when you take all cutting edges into account. If you have a suitable ER32 collet and a collet block then using the collet block in the lathe chuck would help overcome this problem.

The size of a morse taper is easy to figure out from the diameter of the open end. Just look up diameters and dimensions of morse taper sockets. As an example the open end of a MT2 socket is 0.700" . There is also the possibility that you have some morse taper shanks that have a number stamped on the flat of the tang at the end. Doesn't take long to find out if this is the case.

Martin C

I think Pete has figured it correctly in as much as it makes sense that you don't want the weight of the eccentric strap to push the eccentric disk ahead of where it needs to be on the shaft.

Martin C

Maybe it just balances the weight of the metal of the eccentric strap and the eccentric rod. It looks to be quite a weighty mass and it is always acting downwards if there is no balancing weight. this would cause wear at the top but not the bottom of the strap. The direction of the horizontal forces for the eccentric rod are going to be balanced by the backwards and forwards motion of the valve gear.

Martin C

The most basic method is filing. Similarly grinding or sanding (belt sander for example).

Outside radii can be produced by rotating around a pin if there is a suitably positioned hole at the radius centre. Also if there is a hole at the centre you can mount hardened filing buttons and file an outside radius to the size of the buttons.

Inside radii can be produced with drills, milling cutters or hole saws with a suitable diameter but often this will that the hole is made early in the production of the part so that the tool is not only cutting over part of its cutting edges as the uneven forces may cause problems of accuracy and size as well as risking damaging the tool.

I think there will be plenty of examples of these methods on YouTube.

Martin C

I recently made a mandrel for some aluminium parts. The centre was Ø32 so I didn't have the size issues you are worrying about. I put a hole through the mandrel than hacksawed a split along the axis so the resulting tubular spigot could be spread and used a MT2 to MT1 sleeve to spread it when the part was over it. Combined with a live centre this made the mounting solid but easy to release. If you can turn a suitable tapered pin on a piece of stock with a centre drilled hole in the end you could do something similar on a smaller scale if you get a live centre or use Tim's bearing method.

Martin C

There is a Smart and Brown group in groups.io with some of the files from the Yahoo group.

Martin C

The sharp/blunt chisel results in a difference in pressure which is force divided by area. Sharp means a small area so the pressure is higher than blunt with a larger area. Force is mass times acceleration or, in the case of a chisel, deceleration. Force is also the rate of change of momentum. Momentum imparted on the chisel by an impact is mv so if you know the mass you can work out the velocity from the momentum. You can work out the energy imparted at the point of the chisel from loss in kinetic energy which requires mass and velocity to calculate knowing that the chisel stops after a short movement. The one thing that is hard to figure is the deceleration of the chisel as it would take some time to measure the time it took from impact to stationary and enough times to get an average.

The Charpy test, despite being referred as an impact test, is not purely an impact test as the process of bending then breaking a test sample requires that the pendulum does some work on the sample. As I mentioned earlier a true impact does no work as it is considered to be an instantaneous contact that transfers momentum. If you have a hard and brittle sample such as glass then the initial contact is an impact that breaks the sample on contact and so no work is done on it and the change in the momentum of the pendulum is very small so the pendulum swings higher than when a malleable sample that has to be pushed out of the way and has work done on it is tested.

Martin C

Edited By Martin Connelly on 13/07/2023 08:41:50

Funnily enough I was looking at this YouTube video regarding this subject yesterday https://youtu.be/aD7y03rDmFE

The Biggest Lie in Medicine

It has always struck me as crazy that a claim can be made that peanuts (for example) contain as much as, or more than, the same amount of protein as a beef steak so you should eat peanuts instead of steak. A beef steak is easy to digest whereas peanuts are hard/impossible to digest unless they are ground to a fine paste. A large chunk of peanuts must pass through the gut (same as sweetcorn) due to the indigestible cellulose outer shell that the human body cannot digest. Eat enough and you will find out exactly how well these cellulose capsules can pass through you.

As such a lot of experiments regarding the fat, sugar or protein content of foods needs to be taken with a pinch of salt (ha ha) as they do not reflect the body's processes used to extract these nutrients. Even the things you eat in combination makes a difference. Many things we need in out diet are fat soluble and so need to be eaten in a meal that includes suitable fats for it to be absorbed in the gut. An example of something that needs the correct combination of foods is iron, to be absorbed easily you need vitamin C in your diet to avoid anaemia.

Martin C

The plain bronze bearings have an oiling hole that leads from the bearing to a sump underneath to hold some oil. There may be a felt wick feeding oil from the sump to the bearing. This can interfere with spindle removal. does the spindle stop after ¾" by hitting something hard or something soft?

I thought if a bronze bearing was used it would be the same at both ends. Are the roller bearings for a collet mechanism?

Martin C

Do you have a late model that doesn't have the plain bronze bearings?

Martin C

I think impact energy is possibly the energy transferred from the machine to the bit at each collision. In the distant past when I was at school we used to do problems involving collisions of perfectly elastic spheres. It was all based on momentum which I think is mv, mass times velocity. The change in velocity was the important part regarding the energy transfer. So in the case of a hammer contacting a chisel the change in momentum would be because the hammer bounces off the end of the chisel, its velocity is in the approximately reverse direction and probably at a lower value than before contact. At the same time the chisel goes from stationary to moving in the direction the hammer has sent it. If the hammer was in contact for any amount of time then it would be doing work. For a instantaneous contact it is considered to be an impact transfer of energy.

Martin C

Robin, I think force times distance is the work done. The speed the distance is covered gives the rate of doing the work which is power. Kinetic energy is ½mv² where m is the mass and v is the velocity.

Martin C

Car alternators are also based on a 3 phase AC system rectified to DC by a diode pack (6 diodes in the pack). This reduces the AC ripple on the DC output compared to a single phase alternator. When controlled by the inbuilt regulator and with the output connected to the battery there is no need for large smoothing capacitors on the output.

When I worked on gas turbine powered alternator packages we often used brushless alternators. These had a small alternator on the shaft with the external magnetic field controlled by a regulator. The induced current in the rotating alternator coils was then used to power the rotating coils of the main alternator's electromagnet and so produce the output of the alternator in the main stator coils. I don't know for certain but I expect the small alternator's output was rectified. It was probably multiphase as well but I don't know if it was limited to 3 phases or if more were used for better smoothing. I suspect the impedance of the main rotor coils was taken into account to avoid harmonic issues.

Martin C