Member postings for Mark C

My manual feed J&S 540 is in need of a major strip and overhaul. I am having difficulty seeing just how you get the head lifting linkage off/apart. It is shaft driven like all others but it is very hard to see how you get the thing off/apart. If it makes any difference (and I don't think it does but anyway.... ) it has the plain bearing wheel head.

I also need to get at the motor to replace the mounting bobbins and short of getting inside (and I am too big for that) I can't see any easy/simple way of getting at it from front or back?

Has anyone any practical experience working on these things (particularly the head linkage/lead screw and rear mast assembly?

Mark

Mention of Ford "Pinto" engines reminds me that those engines are quite rare, the common 1600 and 2000cc derivatives were actually referred to simply as ford OHC - the Pinto was a 2300cc American engine.

Mark

JS, if that was aimed at me (given the proximity to my post mentioning imperial threads) then I struggle to see your problem with it. I was simply pointing out that old rusted heads on those size nuts and bolts can sometimes be undone with a 14mm spanner - this is something I learned a long time ago working on old imperial motors and vehicles. It might just help someone out in the same predicament.

As is often mentioned on here, if you don't like a subject or the replies - stop reading them or simply ignore them.

Mark

A 14mm AF is just handy if you have old 9/16AF hex to deal with. When the old 3/8th UNF/UNC with 9/16 heads got rusty (which they did a lot if you live near the sea) a 14mm spanner might just get you out of trouble.

Mark

JS, that sounds suspiciously like the draftsman needs re-educating for the real world.....

Mark

Tim, the radius you mention is required to clear the radius in the groove. If you are using ground rings, they often require special grooves to ensure no interference. For rings of larger size (from roughly 30mm up) they are generally made from coiled wire so you get two radius edges as there is no blanked edge on the working diameter.

I have a particular expertise in these if anyone wants to discuss them further (as does "Circlip" - surprisingly with that name! ).

Mark

Bob, you might want to look at a DIN472-72 which would fit a 72mm bore. It would have a free OD around 76.5mm but is thicker at 2.5mm (an extra 0.72mm) and would normally require a groove of 75mm. You could then increase the groove width (it does not matter if it is a little wider as long as the position of the fitted ring is correct - so, wider on the bearing side) or you could grind the ring to match the 70 thou. if you have the facilities. If you grind a metric ring, you will remove the phosphate coating but if it is in an engine it should be lubricated resulting in little detriment.

As John mentioned, you could also try stretching the ring (it is most likely a wire part rather than blanked from strip at this size - unless it is an import from overseas). But that would definitely be "bodging" in my book and if you have a lot invested in the job why take the chance on stressing the ring when you have other options available?

Mark

John,

That may well work but it would be good to know how big the thing is before hand - just bending them is risky unless you know the provenance of the ring. All rings are not created equal, you have probably been lucky!

Mark

Bob,

What size is the groove and what size ring did you intend to fit?

Mark

PS. the ring you have (or most you might buy) will probably be quenched in liquid salt in a process called "Austempering" rather than oil quenched

Edited By Mark C on 20/10/2016 11:37:34

As a point of interest (if you are interested in this sort of thing) it was necessary to create the thread geometry on a fixed reference plane set normal to the helix feature and then create feature axis fort both parts. They then had coincident mates created between the axis and to align the pressure faces the feature sketches were used with a fixed point on one sketch made coincident with the flank of the female thread. This allows me to "easily" reconfigure the assembled thread at whatever geometric conditions I chose.......

Mark

Yes, and I have also got this for Michael...

Ok Jason, it took a while to configure for the new geometry and make the simulation work but I managed to get it to run and here is the result using mild steel female thread and low tensile (175 MPa yield) stud. Everything else is the same so you are seeing a true comparison as far as the FEA is concerned.

Mark

Alan, yes he has - he even posted the pictures but we have moved on since then!

Mark

I was having trouble thinking of the best way to get the contact faces to work in the FEA but I think I have a solution. The solver is busy with the problem as I type....

Mark

Oh, OK I accept. Just need to see if everyone else will?

Mark

PS. I was going to measure some scabby studding in the morning and add to the last drawing for Michael as well...

Edited By Mark C on 15/10/2016 23:16:44

And for all those that might be interested in what the thread looks like with different tapping drills, here is a comparison drawn exactly to scale with a nominal male thread for comparison. The left hand thread is at nominal size, the middle is what it looks like with a 6.8 hole and the right hand one shows the same things with a 7.1mm hole.

Mark

PS, six posts to go and we will have reached 200 !!!

The last one is a factor of safety plot that has been adjusted to show the areas that would fail (I only applied a 5000 newton load to the stud). You can see that it fails how you would expect for a tough steel stud in mild steel thread. If there was clearance it would probably show a slightly different distribution but not vastly so - I don't think anyway?

Mark

And I have spent a spare 5 min. running an FEA on an ideal M8 thread assembly (well it was more like 5 hours by the time I got the mesh sorted and the restraints and contacts working.... ).

This is what they look like;

Rod,

First bit incorrect (there is definitely a right size for the standard thread), second bit correct (quite right, use whatever floats your boat)!

Mark

The pugnacious one