Member postings for ChrisLH

Answering the sketch etc. will take a little time but, looking at the D-W machine, it's a bit more complicated than I suggested because, due to the need to lift the considerable weight of the head, there is a coarse screw thread machined in the collumn and a "nut" to engage it.

Regarding "Clearance .....", I was assuming that there is no requirement to raise or lower the machine head whilst cutting drilling, etc. i.e. the head is clamped whenever cutting is taking place. So, although there may be considerable slop between keyway and key, as long as the key is engaging the same side of the keyway every time the clamp is activated, alignment will be maintained. This assumes,of course, that the keyway is machined parallel to the axis of the collumn, etc.

Yes, that's it

Chris

I had the same problem on my Dore-Westbury milling machine i.e. loss of registration on slackening the collumn clamp.

My solution was to mill a rectangular keyway in the collumn and to provide a captive rectangular key along the lines of the Myford S7 tailstock barrel feature. Clearance is not a problem if you remember to always push the head to the right (or left) on tightening.

Hello David,

My Myford S 7 of similar vintage became noisy about 30 years ago. It turned out to be the needle bearings on the clutchshaft. Replaced with the then current standard "Oilite" bushes and has been OK ever since.

Michael,

You were wrong but, congratulations, you now have the opportunity to be right !

A pair of involute gears can work "correctly" over a range of centre distances.

"Correctly" here means without change of velocity ratio whatever the rotational position of the gears. Just to make clear, that would not be true if you continuously changed the centres as the gears rotated.

If you needed to maximise the range of centres for some reason, involute gears have been designed that could tolerate a 7% change in centre distance and still work "correctly" at either extreme.

Edited By ChrisLH on 05/11/2022 22:26:52

Michael,

I believe the statement to be true but it is dependant on what is meant by standard centre distance. This is all part of a sea of confusion that has built up around involute gears with standard gears, corrected gears, standard centre distance, pitch circle, etc. all of which mean different things depending on who you are.

If the "standard centre distance" is taken to mean half the sum of the blank diameters minus the tooth depth then backlash can be negative or positive depending on the gear details. In manufacture this is allowed for by making adjustment to the cutting depth. Complex formulae are available for calculating these corrections.
In brief, with a given pair of gears if you extend the centre distance, backlash inevitably increases but, as long as the line of contact is longer than the base pitch, an unvarying velocity ratio will be maintained.

But I am not sure of your drft, is this what you wanted to know ?

Michael, your point re. Involute gearing is, I believe, actually the other way round.

Involute gearing will tolerate some variation in centre distance with no change in velocity ratio.

I believe this is not true for cycloidal gearing but because speeds are low in typical applications (clocks) variation of velocity ratio through the meshing cycle at any other than the theoretically correct centre distance is undetectable and therefore tolerable.

I used to use the racking the saddle method and ended up with a bed regrind; my old style Myford has the saddle cut away in just the place where it is needed for the forces generated by this job. I now lock the saddle and use the topslide and linked handle method. Particularly easy to set up if you have a QTP with height adjustment.

I had similar problems at the start and thought they would all be solved by use of a tailstocl die holder. Well, it didn't always produce a good thread. This was traced to the dimples on the o.d. of some dies being carelessly placed and consequently presenting the die to the work at an angle. My current method is to use the hand die holder supported by a rod held in the lathe tailstock to keep the back face of the die square. The rod should have enough clearance in the die holder to allow the die to self centre on the work.

Of course, this only works if you have a lathe. Sad to say I never had any joy threading by hand and eye myself.

I moved from Glos. to Bucks. just over 7 years ago but the memory is still vivid ! Having heard horror stories of removers and even machinery movers dropping lathes, knocking corners off mills, etc., I decided to move the workshop myself beforehand in small loads over a couple months to my daughter's garage close to target. I hired a van and driver so that I had help with the loading/unloading. It's taken me since 1966 to amass the workshop tooling so the last thing I was going to do was to part with any of it. All now safely installed in heated, converted half of the double garage as I don't enjoy the cold, and after all it is about enjoyment.

The rest of the household goods took pot luck with the removers.

John,

You have a PM.

Professor Chaddock made his carved from solid engine crankcase look like a casting by grit blasting with home made kit. You do however need a compressed air supply to make it work. Relevant ME articles p. 456 05/05/ 67 and p. 515 19/05/67. If you don't have access, PM me and I will provide scans by email.

Plus 1 for sneaky Amazon. Like Chris C thought I had rejected the offer of Prime. Not discovered until I found a mystery £7.99 on my bank statement. Cancelled and never used Amazon since.

Consulting my admittedly ancient SKF catalogue your shaft needs to be between 15.005 and 14.997 mm. Quite a challenge for the measuring equipment even before you start removing metal ! Bearings are made to international standards so this applies whatever the make of bearing assuming a reputable manufacturer.

Another possible reason for short crosslide travel as described by OP 17:06:19 is misalignment between feedscrew and its nut. I got heavy handed with my S7 on one occasion and bent the bracket downwards. Very stiff until I bent it upwards.

So I would disconnect the feedscrew bracket from the crosslide to check the latter's freedom of movement. Depending on the result of this test move on to check feedscrew / bracket alignment.

Voith make a large range of railway mech/hydro transmissions. They are used in lots of the diesel MU's running about the country. Probably second mortgage prices though.

RHDR used to have and may still have a diesel twin bogie loco which they use(d) for utility jobs like the regular school run. It may be worth enquiring what power and transmission they use, etc.

Geoff Walker 1

Sounds as if your toolposts rather than temperature are distorting the crosslide. I have the same problem with a long vice on the table of my D-W mill. When I grip a job in the vice the X slide movement goes stiff whatever the temperature. Not helped by the skinny vice base and the unusual tee slot arrangement of the mill - it reduces the longitudinal stiffness of the table compared to the conventional arrangement. If I'm after accuracy I mount the job on an angle plate using G clamps.

Funny how opinions vary. After owning my lathe for 20 years or more I bought a set of quick change tool holders and immediately wished I had bought them 20 years earlier. They avoided the awfull fag of finding and adjusting packing to get tools to centre height every time a tool is changed. They also allow you to continually swap tools around on repetition work. Regarding removing the reluctant screw, I've had success with hammer and small chisel used to drive the screwhead round first on one end of the slot followed by the other.

I have the same early S7 as you but I have not have this problem. As you suspect the friction faces are cast iron and nothing is mentioned about lubrication in the owner's maual and I've never bothered. I had it all apart some years ago in order to replace the needle bearings (which getting rather noisy) with oilite bushes. Only suggestion I would make is you check that the cast iron clutch ring has not been distorted at some stage so that it rubs even with no pressure from the adjusting wedge. I can offer scans of the relevant pages of the owner's manual if you don't have them already. If this of is of interest please PM me with an email address.