Acceptable error on ER25 collet chuck

[Martin King 2Participant @martinking2]

Hi All.

Just had my first attempt at making a backplate for my ER25 collet chuck from Arc. Not exactly a trouble free experience!

First I checked the external spindle of my M7 and it showed about .02mm either side of 0 runout on my Mercer METRIC .01mm dial gauge.

Put the backplate on the spindle and tried to true up the outer rim. There must have been a really hard patch on it somewhere, screeching and chattering like mad, so changed the speed and took a heavier cut which finally got through it into somethng more docile but it did not like HSS at all so tried carbide which was better. Facing was no problem at all and slowly crept up on the correct size register to ;just fit' with a light tap or two.

Realising that I wanted to counterbore (another first!) I measured what I had available that would suit the M8 cap screws and then drilled backplate on the mill with 6.3mm to suit the c/bore pilot. This was not straight forward as the pilot somehow jammed into the hole and detached from the c/bore shaft and stalled the machine! Managed to drive it out and did the other two holes using the pliot to line up and then removing it for the drilling. Kind of OK but I could see the c/bore wandering a bit. Also tricky to line up the other holes as my vice is barely big enough to hold th plate securely so used tool clamps as backup. Finally driiled through 8.2mm clearance.

The whole operation felt 'untidy' which was not what I was hoping for trying out a new process.

Putting the chuck on the spindle and using a Verdict 0.0005" indicator in the taper of the collet chuck I get a variation of 4 units either side of 0 so I guess thats 2 thou either side? Does not sound great but not sure what it should be.

If this is unacceptable where do I go from here please?

Not a nice feeling trying hard to get it right and being disappointed with the outcome but I guess this is how I learn..

Regards

Martin

[Martin King 2Participant @martinking2]

[LambtonParticipant @lambton]

Martin,

I never use counter bore tools for chuck back plate holes. I set up a back plate in a chuck on the rotary table adjust the mill table to position to get the spindle centre line on the PCD for the back plate holes, zero the table and then centre drill and drill with the necessary clearance drill. Then without moving the table change to an appropriate diameter milling cutter open out the hole to the correct depth. No problems then with anything jamming and no alignment problems as the work is done at the same setting. Just repeat the process for the remaining holes at the necessary angular displacement.

You might like to check the "as made" accuracy of the collet chuck register by gripping a length of material in the 3 jaw and turning it down to say 12mm then mount the collet chuck on this stub mandrel with the register towards the tailstock.. Use a DTI on the register bore and face to detect any inaccuracy.

[Martin King 2Participant @martinking2]

Hi Lambton,

Thanks for that info.

I guess I can still use your method on the same backplate, just put the holes somewhere else!

Asi in my OP is the runout unacceptabl;e for a 70's ML7?

Are counterbores not any good then? Should the pilot detach?

Martin

[Tony Pratt 1Participant @tonypratt1]

Hi Martin,

My 1960's? Super 7 has a spindle register run out of less than .0005" which I am happy with, I personally wouldn't be happy with your figures but how much effort do you want to put in to correcting it & are you capable of such work?

I used counterbores all my working life with no problem so yes they are 'good', never with detachable pilots though, I have also used milling cutters many times to make counterbored holes with equal success.

Tony

[Martin King 2Participant @martinking2]

Hi Tony,

I would like the machine to be set up properly but doubt that I have the necessary skill level to do it myself.

How would I go about getting this done professionally please?

Martin

[Tony Pratt 1Participant @tonypratt1]

Hi Martin,

A new spindle would be my first step, have a look on the Myford website to see if they are still available.

Tony

[LambtonParticipant @lambton]

Martin,

There is nothing wrong with counter bores I just do not use them for this application.

It is vital that the ER chuck (or any other chuck) is located on the back plate by the register alone and not the bolts that are only there to clamp it to the back plate. If the fixing bolts are not totally clear in their holes they will cause inaccuracy.

[Martin King 2Participant @martinking2]

Lambton,

The bolts were a bit tight in their holes when I bolted the chuck to the backplate, so will take them out to 8.4mm from 8.2mm and see if it is better.

Martin

[David ColwillParticipant @davidcolwill19261]

I have counterbores that came from MSC J&L, they do seem to have ridiculously large pilots on them. The M8 is 9mm and the M12 is 13.5mm. I have thought about mounting my spin indexer on the surface grinder and grinding them down a bit but have wondered if there was some standard or other that I don't know about. I locate most important holes with a DRO so really don't need this sort of clearance and can always open the holes out if needed.

I think I've just convinced myself!

Regards.

David.

[Neil WyattModerator @neilwyatt]

As Lambton says the fixing holes should be well clear of the screws to make sure that its only the register that locates the chuck.

This source suggests going up to 10mm for a 'free fit', I wouldn't use less than the medium fit for anything that relies on a register, dowels or similar for location.

Neil

[AjohnwParticipant @ajohnw51620]

You only need to provide clearance to suite the precision of the hole placements with a minimum of 0.015 / 0.4mm but remember this assumes that the holes are square on to the things they are fixing.

John

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[Martin King 2Participant @martinking2]

Well, something learned today!

Opened out the holes to 8.5mm and now the runout is less than 1 thou!

Good enough for most that I do and probably the limit of my skill at the moment. Thanks for the help folks

Martin

[Martin King 2Participant @martinking2]

Should counterbores have removable pilots ?

Martin

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