Member postings for ChrisLH

I have the wobbler type and have never thought of oiling it; seems to work all right without. If it did need lubricating I think I would try the old bookbinders trick for attaching gilding to covers, they use (or used) the grease off the end of their noses !

Mine is an Optibelt as recommended by Myfords at the time (about 40 years ago) that I had the bed reground.

Part No Z870

In response to Simon Williams 3, for involute gears using standard hobs (20 PA) the minimum number of teeth for satisfactory meshing is 10. However as for all gears with less than 20 teeth, the gear diameter would need to be increased above the usual (T+2)/DP.

I was told by an ex Smiths employee that, at one time, they made clocks using involute gears.

To accomodate the limitation on tooth numbers imposed by the involute system most clock gear trains would of course need to be redesigned.

As an aside, gear pumps have been made using gears with only 8 teeth but these were made using special involute hobs of 25 PA (?) with non-standard cutting depths.

Although clock and watch gears are referred to as Cycloidal, I believe they are only approximately so. For example, it seems unlikely to me that the inner part of the contact faces of 6 leaf pinions (the hypocycloids), which are straight in practice, are theoretically so.

But I'm no expert so please feel free to put me right.

I also have an Ortec 2 axis DRO purchased 26 years ago and still going strong. The display unit did go on the blink back in 2015. I got in touch with Ortec and he (only employee) invited me to send it back for invetsigation. Came back a few days later, fully functional. Charged me precisely nothing ! Not many of those about.

Interesting. How else should one unscrew a M-B 4 jaw chuck other than using the chuck key in the screw sockets ? I bougtht mine in 1966 second hand with the lathe and have always used this method without apparent detriment. Screws show all the signs of being steel, sockets are hex. though.

George Thomas in his book "The Model Engineers Workshop Manual" reported on measurements of run-out he did on drill chucks he owned (page 114). The US made Jacobs chucks he measured varied from (inches) 0.0012 to 0.0003 close to the jaws to 0.0022 to 0.0003 at 1 inch away. Pretty good !

Rob,

No, the holes are not countersunk.

John,

Surprising that later screws are so much longer than older ones.

My S7 is rather old which might make a difference (SK 2142) but here are the dimensions of the screws I have extracted from the second and third holes, both the same.

Overall length 1.875

0.250 BSF threaded length 0.650

Slotted for flat blade screwdriver on the threaded end

Plain end approximately spherical

Re. gun/cannon on aircraft, could it be that guns fire inert missiles whereas cannons fire shells containing an explosive charge which detonates on impact ?

Thanks for your replies gents.

Martin, this makes sense and near enough to go ahead and buy one.

George, not quite sure of your drift. The web address brought up polishing spindles.

D31k, see above, bullet to be bitten at Screwfix tomorrow. (more money but easy returns)

I'm looking to buy a tube bender for 6, 8 and 10 mm copper tube. An apparently identical item is available from Screwfix, Wickes, RS, etc. in a variety of colours and prices but nowhere can I find listed the bend radius of the bend former, something I need to know for my project.

If someone who has one of these devices could pass me this information, I would be very gratefull. TIA.

It seems to me that the (preloaded ?) ball thrust bearings locating the shaft in the z direction have some slight assymetry in their races causing the balls to track in a slightly different position depending on direction of rotation. Should perform OK though as the spindle usually only rotates in the same direction.

I also have the single bolt type and confirm that it is not very secure having slipped on occasion. Presumably the two bolt type is an improvement (why else change it) but I don't, at the moment, have an explanation of why it should hold better given equal clamping forces. Perhaps the smaller diameter of the two bolts allows higher clamping loads under normal spannering conditions. Any other ideas ?

Regarding Tim Hammond's observation re. tappet chest covers, could it be that the OP's engine was an economy version where black painted pressed tin had been substituted for polished cast ali. ?

In favour of the Triumph, the front fork damper adjustment appears to be in the forwrd position as in the OP whereas the BSA is rearward ?

You just need to buy a Casio fx-85GT Plus calculator. Annoyingly for most uses, it does its work in fractions and you need to press the S~D button to convert to everyday decimals. May also apply to other Casio models.

The usual advice for full size engines is to hone the bores with not too fine a stone. The idea is that the scratches retain lubricant which would be swept away if the finish were too good. I'm not able to put numbers to this which is just as well as measuring surface finish is not something us amateurs are usually equipped to do !

There is a very nice miniature version of the Big Ben gravity movement in the church tower in Askrigg, N Yorks. Made by Potts of Leeds. I have no other info. unfortunately.

Agree with all of the above but would like to add :-

The annoying habit of cameramen who continually cut to the presenter's face instead of giving us time to see what's happening with a craftsman's hands or to study a map, etc.

Cannot comment on optical as I haven't tried it. My machine is fitted with the common type of DRO consisting of a solid steel bar with a cursor / read head sliding along it (magnetic ?). Both quill and Z axis are so fitted. I use the quill readout a lot and the Z axis one much less so partly because I don't altogether trust the Z slide (it moves a couple of thou in X and Y when I lock it). However, after a while and if there is a lot of swarf about this type of DRO starts to misbehave (mainly X and Y axes) and needs to be stripped and cleaned. However I have found that the 2 inch square, clear plastic tubing that forms the packing in which curtain rails etc. are supplied can be cut in half along its length to form an effective barrier to swarf. It is flexible enough to allow the buttons on the read head to be depressed. Some form of bracket needs to be made to support the shield at its extremities.