Member postings for lfoggy

Can't answer your question but the project looks really interesting. is there any information about your engine?

Sounds like progress !

In my expereince it is virtually impossible to achieve an optimal escapement by hand filing or machining to a scribed line. You always need to do some adjusting. How long you spend adjusting depends on how much of a perfectionist you are.....

With a recoil escapement it is very difficult to completely eliminate drop but it should not be excessive otherwise the pallet face won't last and consistency will be affected. The drop will always be visible on careful inspection but should not cause a noticable visible jump forward in the seconds hand. As for recoil, there should be a clearly visible degree of recoil apparent on the seconds hand. Do you have a jig on which you can test the escapament and vary the distance between escape wheel and pallet arbor? This is very useful. You can then alter this distance to detmine the optimal positioning. If you haven't yet hardened the pallet you can gently squeeze it in a vice to reduce the distance between the pallet faces which can help as well.

Maybe post a video of your escapement in action?

There are lots of reamer tolerances but finding anything other than H7 is not easy. You could try Taylor & Jones of Sheffield. See last page of document below.....

Taylor & Jones

Most of my projects are full of hidden embelishments like that !

My cutters have flat ends and seem to work OK. I am fortunate to have a Deckel SO tool and cutter grinder clone. This tool can grind accurate squares and hexagons in HSS really quickly and easily. Happy to assist in grinding a cutter for you if you.

I'm definitely no expert on this topic and can only refer to my experience as an amateur. My lathe a a very good condition Myford 254 and my cutters were made of accurately ground HSS. The Hemingway tool is very good for cutting squares in brass for my clockmaking and will also cope with 6mm hexagons in steel. I agree its small in size but even if I had a larger broach I doubt my lathe would be up to pushing it through the workpiece to be honest.....

Edited By lfoggy on 15/11/2019 20:31:14

I made one of the Hemingway rotary broaches with a parallel shank which I hold in a drill chuck on the lathe. Works fine for squares or hexagons up to about 6mm. You have to use a lot of pressure to get it to cut so no chance of the morse taper coming out.

If you are going to try to broach 3/8" square holes you would need a hefty lathe. I think.

I am going to treat my lathe to a new high quality three jaw chuck. Looking for a 125mm chuck with a D1-3 Camlock fitting. I want new chuck rather than second hand. Would be grateful for some advice.

I’m thinking a Pratt-Burnerd ‘super precision’ or maybe a ‘Grip-Tru’. How consistent are the ‘super precision’ chucks? PB website says max runout 25µ. What about the Grip-Tru - is that worth the extra complication compared to a good standard scroll chuck? Bison do a premium scroll chuck that claims a maximum runout of 15µ which seems unrealistic for a scroll chuck but then it is very expensive. That would be a three-jaw chuck with the concentricity of a collet system though.

Also considering two-piece jaws to allow aluminium soft jaws to be fitted more easily but have never used these so wondering how practical they are.

I have now ground the chuck jaws using the setup below.

Grinding wheel rotating at 5000rpm (too low I know) and lathe chuck rotating at 1000rpm. Removed 0.02mm at a time. Lots of sparks but otherwise uneventful. The finish on the jaws was very good.

The chuck is new and the jaws are a very firm fit in the slots with no discernible movement so I don't think much 'cocking' has taken place although i fully acknowledge the logic of grinding them tensioned in the closed direction.

Testing the newly ground jaws as below shows that the clamping face of the jaws is at right angles to the slots to within <0.01mm as below.

I know some people suggested a slight taper on the jaws which is logical but hard to achieve so I just ground them straight.

I can now hold a test bar securely and accurately in the chuck - much better than before. I'm very pleased with the result and was surprised how easy this was to do.

The jaws are a firm sliding fit in the slots with no discernible play so I am hoping that they will remain aligned during grinding.

I don't have a surface grinder but another option is to use a cupped diamond wheel in the milling machine with the jaws held in the milling chuck. I have used this setup to grind small amounts off hardened components in the past and it has worked.

I will try to get this sorted over the weekend and will post an account of success or failure....

In my experience its the corner that wears out first and the edge of the flutes stays sharp for much longer. I usually sharpen just the ends but periodically give the edge of the flutes a very light grind. This does of course change the diameter of the cutter slightly.

I recently purchased a Chinese copy of the Deckel SO tool and cutter grinder which can grind both ends and flutes of cutters with ease. Best thing I've bought for the shop in years...

Quick 'back of the envelope' suggests that at 1000rpm there will be a 50N radial force on each jaw, i.e. 5Kg . Cutting forces will generally be in the same direction as well. Maybe a bad idea though ! I'm sure a rummage through my scrap box will unearth a suitable ring against which to clamp the jaws.

I was planning to position all four jaws the same distance from the centre using a dti, then set the chuck rotating and grind all four jaws at once with a pneumatic die grinder held on the cross slide and rotating in the opposite direction to the chuck. I was assuming that centrifugal force would hold the jaws in position. I only need to remove 0.1mm.

Does that sound reasonable?

Many thanks for all the suggestions. Sounds like I just have a 'Friday afternoon' chuck. I'm told most days were Fridays in some factories in the 70s and 80s !

Will try regrinding the jaws.

The chuck body runs true on all faces to <0.01mm runout with no distortion of the body. There is nothing to suggest the jaws have been reground (but who knows).

I've removed the chuck jaws and held them with the clamping face against a true vertical surface as below. Running a dti along the slot in the jaw confirms that the slot is not at right angles to the jaw face. All four jaws are out by the exact same ammount. This seems very odd. That degree of consistent inaccuracy cannnot be manufacturing error.

I've already stripped, cleaned and re-oiled. Apart from some congealed grease there was nothing to remove, not even a speck of swarf. The register is an integral camlock D1-3 and the chuck body runs perfectly true. All looks good apart from the issue described...

I've recently acquired an 8 inch Pratt Burnerd 4 jaw independent chuck. It is stamped 'Made in England' and I think it was manufactured in the 80s. It seems to be unused or virtually unused as there are no marks on the chuck whatsoever and the D1-3 camlock fitting shows no signs of ever having been attached. The jaws have a perfect ground finish and are unmarked with no detectable play in their slots. When I fitted the chuck to my lathe to test trueness I found the chuck body to run true to <0.01 runout.both on the periphery and on the face. The clamping surface of the jaws however are not parallel. They are the opposite of 'bell- mouthed' as in the pic below. The taper is consistent on all four jaws. This may not matter too much for many applications but is definitely apparent when trying to grip a long and accurately machined workpiece.

What is the explanation for this? Were the jaws deliberately given a taper to accommodate wear or do I just have a badly made chuck? I am suspecting the latter.

I do reaslise that this taper would be easy to correct by the in situ grinding of the chuck jaws and I may well resort to this.

Problem there is the thieves, when they realise they have nicked a can of old engine oil, will just pour it down the drain. You might as well just pour it down the drain yourself....