Member postings for Martin Connelly

A lot of taps have centres drilled in their drive end. If you drill a hole in a workpiece on a mill or drill for a tapped hole you leave the workpiece in the drilled position, put the spring centre in the chuck or collet of the mill or drill. You then position the tap tip in the hole and bring the spring centre down to the point where the centre is in the tap's centre drilled hole. This aligns the tap with the drilled hole to ensure the thread is produced evenly without an angle to the workpiece.

Another use is when setting up a centre popped hole in a workpiece in an independent chuck on a lathe. You put the spring centre in the tailstock, trap a plain centre between the centre pop and the spring centre and put a DTI on the centre. As the chuck is rotated the eccentricity of the centre pop is followed by the centre and shows up on the DTI. Much easier than trying to set the centre pop to a tailstock mounted centre or by eye.

There are probably other uses as well that other people can suggest.

Martin

If we are picking holes in this then cos(45) does not equal 1, Tan(45) equals 1 and cos(45) is 0.707 (square root of 2).

Martin

An adjustable reamer may be of use in this material. You only want it slightly over size to make sure it does not cut a lot off, just a very fine swarf that is more like dust. Keep it cool and repeat a few times at the same setting until it stops cutting.

Martin

There are plenty of articles on the internet on making a home made one. The simplest to make has a round piece of HSS in a hole drilled at a suitable angle with a grub screw to secure the bit. This will allow you to make a boring bar to suit your job to get the best rigidity.

Martin

You could consider a 3mt to ER32 collet holder. ER32 collets hold with a parallel action and so grip parallel shanks well. They are also more likely to have lower runout than an end mill holder that must push the cutter to one side of the hole to secure it. You also have the option to vary the stick out of the cutter within the limits of the shank. You can buy additional collets as required to keep initial costs down.

There is a thread on this subject called "ER Collet chuck or normal Morse Taper Collets", not sure how to link to it.

Martin

I have access to a CPS20 ring rolling machine in Lincoln. Should be able to do this without a problem. Where are you?

Martin

I agree with Adrianh. Timing belts make an easy set up. All that is needed to adjust the belt are slotted holes. You can have a 1:1 ratio on timing belt pulleys or increase or decrease the ratio. If top speed is not important because it is not a production environment then lower speed can give higher torque. If the stepper motors you are using are going to be open loop then higher torque is always better to avoid missed steps. Steppers with feedback, such as Leadshine hybrids, can give an error signal from missed steps but with open loop it is always a possibility. Timing belts also increase the options of the motor position relative to the leadscrew. This may not be a consideration for you but for people with restricted width setups it can be a bonus. The y axis motor can often be tucked under the table rather than having it stuck out in front.

Martin

I know the motor seems to run fine with no load but struggles when loaded. I would check the brushes are not worn to the limit where they make some contact but not enough for high current. Brushes worn to the limit will give the problems you have and may be a cheap and easy fix. You can nearly always find a suitable brush even if it needs filling down to fit the brush holder. Check to see if the spring pushing on the brushes is hitting a part of the holder or if the connecting link wires (if the brushes have them) are not pulled up tight.

Martin

If the blow lamp is cold and pressurised you should be able to squirt some paraffin out of the jet.

If you pressurise it before it is hot enough and the meths around the heater loops is still burning you can shoot a jet of burning paraffin out. I have seen this done with a Primus stove which works on the same principle, straight up onto an awning that was rapidly destroyed , so be careful where you point it. Fun in the scouts, good job it was not a tent.

I don't know what instructions you have but it should include reference to the vent. Heat the thing up with the vent open, just before the meths burn out close the vent valve and apply a small amount of pressure. The paraffin should be vapourised and burn as it comes out of the nozzle, if it remains liquid the heating process has not got everything hot enough so open the vent to release the pressure at that point. Do not add more meths unless you are absolutely sure there is no flame or nasty burns may result. If the paraffin is vapourised and burns pump a bit more but not too fast, you don't want to blow the flame out, gradually bring the pressure and thus the heat up to a point you can use the blow lamp. My dad always preheated the burner area with a gas hob to make the lighting easier, this is without fuel in it for safety. My uncle had a petrol blow lamp and that sounds far too risky to me, cold paraffin is a lot harder to have an accident with.

Martin

There is nothing in the world that is truly rigid. If you put an indicator on your test bar and push the bar towards the indicator you will find it takes only a small force to give a deflection at the tailstock end equal to your taper. Think about how much force is required to push the cutting tool into the work piece and they are probably similar. More force is needed with relatively blunt carbide tipped tools than a freshly honed sharp HSS edge. What are you using? Also a suitable steady will push the workpiece to keep it from deflecting if you have one.

I think the test bar is telling you that the spindle is correctly aligned with the bed and the taper is caused by deflection as suggested earlier. Light cuts with a blunt tool are more likely to rub the surface than cut it if there is deflection.

If an out of true chuck caused a taper then we would all have binned all our 3 jaw chucks a long time ago. As discussed in another current thread 3 jaw chucks are unlikely to hold something perfectly aligned.

Martin

If you had soft jaws for your 3 jaw and machined them to size you can still get run out away from the chuck if you are not careful when setting the part in the chuck. The parallel grip of opposing jaws in a 4 jaw chuck reduce setting errors like this. If you machine a part in a 3 jaw chuck and mark its position to replace it back in the same place at some future time you will more than likely find it will not be running true when reinserted in the chuck.

Martin

KWIL, are you responsible for anything else? I'm thinking of the battery location as something to moan about.

Martin

Remember to get a motor that has the same RPM at 50hz as the motor you are replacing. The number of poles of a 3 phase motor give different nominal speeds.

Martin

You can remove the skin with a belt sander or a grinder with a gentle touch if you have one then minimum machining to get the surface flat. If you have a carbide cutter this will tackle the skin better than hss. The depth of cut will depend on how flat the surface is to start with. The skin may be 0.5mm thick but have a height variation of 1mm depending on how well the casting has gone.

It is often only the edge that causes a problem, once past that the machining goes easily. Once you have experience you will not worry too much about it in the future. If you have a fly cutter and a lathe do you have a carbide tipped lathe tool you can put in the fly cutter? Otherwise a carbide end mill or slot mill will do the work but may take more passes.

Martin

Would you trust a modified test bar? There may be residual strains from heat treatment that will be released by grinding off the material that is causing the problem. I think you would have to get the whole thing carefully checked after modification and it may need complete regrinding to get back to the original specifications if you want to keep the existing centres. If you abandoned keeping the end with its centre just cutting the end off should not cause the rest of the bar to distort. You may though have a problem in that the original specification was with the morse taper supported over its whole length. Removing part of the taper may change the setting of the bar in the socket.

These are just thoughts and the only way to find out if it is possible is to do the grinding and check the bar afterwards.

Martin

Jon, the most recent interpretation of the PED that I have seen is that the 1 1/2 times test pressure should be applied to the safety valve release pressure not the operating pressure. This makes the test pressure higher than just using expected working pressure as your starting point so is a more rigorous test. It is because it is possible for the operating pressure to be at fault at higher than nominal pressure and the system can still work as normal.

Martin

I think pressure vessels or items that are pressurised under normal operation but are not covered by the PED due to exemptions are usually covered by other regulations. Boilers and gas turbine casings are examples.

Martin

It looks like it is designed to pull something past the centre plate or to pull itself along a surface. Does it help lift carpet, tiles or other floor covering?

Martin

Vertical alignment of round column machines:

Another work around is to have a variety of tool holding options. For example if you have an R8 spindle and plenty of R8 collets you can put long tools in them, mid length tooling put a 16mm R8 collet in with an ER32 collet holder with a 16mm shank and for short tools put a 16mm collet in the ER32 chuck and put an ER11 chuck with a 16mm shank in that. There may be run out issues if the quality of the various parts is not great but they will all share the same centre of rotation. It is also useful to be able to use ER11 in tight spots where a larger collet or the spindle itself may be too big for access and you are using small drills.

You can loosen the R8 collet and move the ER collet up and down on its parallel shank as well if you plan ahead and set it to a suitable starting position.

Martin

Mix a small sample of paint and white spirit and paint a small test patch somewhere. You will know then if it works as well as you want or not as the case may be.

Martin