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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: Tailstock height
01/03/2016 23:23:12

Does the height difference change if the tailstock barrel is extended out or retracted? Change like that would indicate that the tailstock was not parallel to the bed and that there may be some swarf or other debris stopping it from seating correctly. I would be wary of milling the tailstock, too easy to go too far. Less aggressive material removal may be slower but safer.


Thread: Is it carbide?
28/02/2016 14:07:54

If you have a spring scale you can weigh the bit when fully immersed and the difference between the immersed weight and the weight in air will give the weight of the displaced water. The air weight divided by the displaced water weight should give density.


Thread: Drill and tapping flywheels to take an M3 grub screw.
25/02/2016 10:42:48

I have used ER11 collets in a Ø16mm shanked collet holder to hold small tools for accessing setups like this. It will not give enough clearance on very small flywheels or ones set at a small angle but is better than a full sized chuck for some jobs.


Thread: Tongue in cheek
25/02/2016 10:37:16

The division of a circle into radians was missed out. There are 2 x pi radians in a circle. The definition of a radian being the angle of radius r whose arc length is r. The useful part of this is that when working in milliradians a good approximation of rise or fall at a given distance horizontally is 1mm per metre per milliradian for small values of milliradians.


Thread: milling cutters
21/02/2016 00:28:15

The shanks can be turned down in a lathe as long as the cutters are not solid carbide.


Thread: Sourcing Worm and Wheel Gear Arrangement
19/02/2016 08:40:06

JasonB, you are of course correct about 0.707 and 1.414 and the square root of 2, I should have said 0.707 is the inverse of square root of 2. More haste more mistakes applies to everything.


18/02/2016 14:31:10

Further to this 2:1 ratio in similar sized diameters for skew gears:

The angles in the example above are found from the inverse tan of 0.5 and 2 (half the speed one way and double the speed the other).



The angles have been rounded to 3 significant decimals. If they are rounded to 1 decimal you get the angles stated earlier.

Hope this helps anyone considering other possible ratios.


Thread: A Spring Centre - March 2016
18/02/2016 14:21:55

Here are some pictures of what I tried to explain above.



18/02/2016 14:10:14

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.


Thread: Sourcing Worm and Wheel Gear Arrangement
18/02/2016 13:55:04

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).


Thread: Accurate hole in Delrin?
18/02/2016 08:12:09

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.


Thread: Boring bars
16/02/2016 14:25:07

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.


Thread: end mill holder
16/02/2016 14:13:49

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.


Thread: Bending brass angle
16/02/2016 14:00:10

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


Thread: Cheap stepper motor couplings?
15/02/2016 14:23:04

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.


Thread: Retired American living in France with a new toy
11/02/2016 14:56:20

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.


Thread: Parafin blowlamp
23/01/2016 19:27:53

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.


Thread: Harrison L5 problem
23/01/2016 15:37:05

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.


Thread: To grind or not to grind...
23/01/2016 10:49:34

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.


Thread: new member PHANTOM MAN
22/01/2016 15:54:34

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


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