MadModder

For all those who would like to use an old fridge freezer compressor as a small air compressor, I may be able to save you some trouble. I had a small compressor (Wolf Cub) in the garden shed used just for blowing up garden tractor tyres trailer wheels etc etc. this sort of thing:-
 

It used the very common pressure regulator controller widely available  (I know now) new for under a tenner on Ebay. Apart from the noise it worked OK for a few years until it didn’t: motor u/s, so bought another one for circa £50 which was even noisier – still for occasional use it would do. They both used the very common pressure regulator switch widely available new for under a tenner on Ebay.:-
 
 

In the garage/workshop I had a couple of old fridge compressors from long ago scrapped fridges (that’s wives for you: “It’s the wrong size, shape, colour it’s got to go etc etc.”) so I thought I’d couple one to the tank & regulator etc from the deceased Wolf. Come in handy as a blow gun for the lathe & mill without the noise of the big compessor - easy as pie I thought – all fitted with the aid of a couple of custom fittings turned to convert the fridge pipes to BSP etc. Emptied about 100ml of oil & refilled with 10W30 & away to go. No tank pressure all air leaking from what I discovered to be the unloader valve situated between the electrical glands beneath the switch.:-
 

 Cue a world of pain as I decided to dismantle the pressure switch to see how the unloader worked  literally HOURS later I finally got the little electrical switch return spring back in place & could refit the switch. - Still leaking & no tank pressure.
Took off the regulator switch & all guages & cleaned all thoroughly reassembled (now used about 20 yards of PTFE tape!) Result just the same.

Went online & finally found the reason: apparently there is not enough oomph in a fridge compressor to close the unloader valve against its (puny) spring so the valve needs modifying to remove the spring – see this video from about 4:40 for how to:-



Drilled out the valve keeper, removed the spring, refitted the core with a retainer of vac line from an old Merc & FINALLY all was well.

So – if you are doing this, since these regulator switches are so widely available:
1 Be aware of the need to modify the unloader valve if it  leaks – I assume it works as is for some people, since i could only find one reference to this on t’internet.
2. Unless you are a Japanese schoolgirl with uncommonly long strong fingers, do NOT dismantle that bloody pressure valve If I’d known they were £7.99 delivered on Ebay , I would have introduced it to Mr Sledge & his friend Mr Anvil.

With that controller, you don't really have to know/worry about the backlash. This is only important when you reverse the direction of movement. You program your favorite direction in the parameters and work always in that direction. When you reverse, the controller will go past the desired position by the amount of steps programmed and re-approach the final position on the correct count. If in doubt, program a high value and it will be ok.

It depends what you are doing with the table. If you are simply positioning a work piece eg to drill holes in a plate, the friction of the movement combined with the backlash compensation will probably eliminate most of the backlash - although any non axial machining load may move the table within the unconstrained backlash angle, as there is nothing actually holding the table from moving. But worse than that, if you are milling a feature in such a way that the cutting forces try to move the table further in that direction, you may actually double the total backlash by applying "compensation".

A similar-ish issue arises on linear axes when you transition from conventional to climb milling, which can happen simply by increasing the optimal load (width of cutter engagement). The forces on the ballscrew are reversed, yet the compensation isn't. You can feel this effect for yourself in manual milling in "conventional mode" - there comes a point where increased engagement results in negligible feed force being required and further engagement beyond that point results in the work "self feeding" or pulling itself into the tool. At that point if you have backlash, it will result in a sudden step feed into the tool as that backlash is suddenly taken up, which can be disastrous for the tool.

The bottom line is that you are much better trying to minimise / eliminate the mechanical backlash in the first place rather than hoping to rely on some "clever" software to magically dial it out for you.

Having said all this, still feeling under the weather,in fact I think this weather has a lot to do with it! I definitiely feel the need for some sunshine. Have been told about the shingles jab, but declined, and also (possibly unwisely) declined a covid booster! I did get covid for the first time a few weeks after the second jab, but was nowhere near as ill as I was after the first covid jab! That put me in bed for a week! Roll on sunshine!
Phil

Over here I had the shingles shot and the follow up a few weeks later I would think your wife should ask why.

Good news! I have today tested negative for covid, so will go back to the workshop to carry on installing the new heating next Monday! Normal service will be resumed on the following Saturday at 4PM! Feeling a lot better but still got the hangover cold that my brother was suffering from  when I caught it off him.......maybe, who really knows!
Thanks for your patience!
Phil