HNC Varigrip collet closer

[Artitus]

Good morning,
Do any of you knowledgeable people out there know if it is possible to buy spare parts for this closer? The drawbar extension is worn making it impossible to get an adequate air seal to the phosphor bronze bush. We have tried high pressure oil seals as a replacement but they created too much friction and the bearing overheated.

We could buy a complete assembly from Hardinge but we are poor! The shaft could be hard chrome plated and reground but at a cost of £358!

Was Varigrip a Hardinge product or is the manufacturer still in business?

Any help appreciated.

[JP Hardinge]

I have one on my 1980's vintage CHNC, and I noticed the air lube system was just not getting enough lube to it. It leaked air horribly as I understand they all do, plus make a lot of noise.

Well the other day I squirted Ballistol lube oil into the front and rear bearing edges of the collet closer while it was turning and it immediately stopped leaking air and it stopped making noise. Quiet as a mouse, and has stayed that way for days of use.

I think one of the problems with the vari-grip is it just does not get lubed adequately with the Hardinge air system.

[Artitus]

Thanks for the response. I think ours is past a squirt of oil! There is an oil feed through the air line which escapes with the air. We costed hard chrome plating and grinding the extension but that was comparable with a new drawbar!

We have plans for a more conventional closer using a cylinder on the tray and a cranked linkage to a sliding collar. We are hoping to retain the original cylinder and piston less the seals to keep the drawbar located in rotation in the spindle. There should be no air leaks with this and the tolerances are a lot more open.

I'll report back if anyone is interested.

[JP Hardinge]

Please post your results. THere is very little info on the net about this collet closer.

I'm still convinced there is not near enough oil moving through the air system for the unit, on my lathe anyway, for it to stop leaking and making noise just with a squit of oil.

I wish there were more users posting about these Hardinges somewhere. There must be many machines being used out there.

[Delw]

is this the collet closer with the round bronze cylinder and 2 big leather seals in it? they were used on a lot of hardinge machines ahc's.
if it is they are very easy to fix and even modify.
if you can't get the seals from hardinge( 25 bucks a pair I think) you can soak the leather seals in oil ( when they are unassembled )for a few days and it will expand them back out. there good for another year that way.

[Artitus]

Originally Posted by Delw is this the collet closer with the round bronze cylinder and 2 big leather seals in it? they were used on a lot of hardinge machines ahc's. if it is they are very easy to fix and even modify. if you can't get the seals from hardinge( 25 bucks a pair I think) you can soak the leather seals in oil ( when they are unassembled )for a few days and it will expand them back out. there good for another year that way.

No it's not like that.

The drawbar has an extension that passes through the ali cylinder/piston. The extension is in fact a sleeve over a hollow shaft (to allow the workpiece to pass through) which has two shallow grooves in it. These grooves are 180*apart, extend into the cylinder and connect through two holes separated longitudinally by around 1/2"in the sleeve to the outside world. A bronze bush with internal grooves lines up with these holes and is connected to feed air lines. Air into one, passes into the bush, along the groove and operates the cylinder. Air into the other, pushes the piston in the other direction.

(At this point I realise how useful a picture would be!).

The bronze bush is accommodated in a 3" diameter ali housing that carries conventional ball races each end.

The only way air is constrained is by the close fit between the bush and the drawbar extension. After many years of service, wear on the extension allows air to escape into the bearings. Even though there are small bleed holes behind the bearings, there is a lot of air passing through the races.

We tried conventional high pressure oil seals but these gripped the shaft under air pressure and caused the whole assembly to overheat. We tried ptfe rings each side of the bush grooves but these were either too tight and overheated or too slack and allowed too much air leakage.

Hard chrome plating followed by grinding might have returned us to the original performance but was expensive and I was never impressed with the Harding solution.

We are now working on a short air cylinder mounted on the tray at the end of the headstock pushing upwards on a cranked arm connected to a sliding sleeve on the drawbar extension (like conventional manually operated collet closers). I hope there isn't a good reason why Hardinge didn't go this way! I'll keep you posted and thanks for the interest.

[JP Hardinge]

Good luck with the mod. Will you be able to operate your cylinder by CNC?

One thing I have learned on the net it seems it may not be worth putting the money into rebuilding these. Also it pulls the part back, at least mine does when you place stock in a collet and line it up with a bar puller, it pulls it back as it tightens down.

Why would hardinge design it to pull back? I have a manual collet closer with lever arm on my 1951 hardinge manual chucker and it doesn't pull back. I works flawlessly. In fact, I kinda wish I had it on the CHNC.

[JP Hardinge]

Heads up:

http://cgi.ebay.com/Hardinge-phnumat...item414d0072df