Truing a ER40-R8 adapter

[taiwanluthiers]

I got a really cheap (20 dollars not including shipping from Hong Kong) R8-ER40 adapter. Everything seems to check out, but for whatever reason the runout is horrible... about .005" or so. I checked everything and it looks almost as though the ER40 chuck itself has flawless runout, and same with the collet, but there appear to be a problem with the R8 side of things... I initially shimmed it with tape which reduces the runout to about .001" or under, but problem is the tape falls off meaning I had to start all over again if I ever have to remove the chuck.

So what I did was, like before when shimming with tape I would use a dial indicator to find out where is the thing out of round. But instead of adding tape to the opposite side to correct the runout I took a sharpie and marked on the cone section of the R8 arbor and carefully filed the marked area until the sharpie was gone (only a little remain in the pore of the steel). I would then reinstall the chuck and check the runout once again. I would then make minor corrections by finding out where it's out of round and filing a small amount of material off and just keep going. I was able to reduce the runout to under .001" by doing this...

In case you're wondering, I checked the spindle and it has no discernible runout (less than .0005") so I know that wasn't the problem. Since R8 shaft has a spline it will only go in one way, meaning it can't be rotated in such a way to throw off what I just did (this probably will not work for MT3 because MT3 has no spline)

Similar Threads:

• ER40?
• Truing the center slot?
• Truing chuck jaws
• Truing a 3 Jaw Chuck
• truing lathe chuck jaws

[Superman]

When you say "runout", was that measured on a round bar held in the collet ?

I may have corrected it a different way ( not suitable for higher speed spindles, due to out-of-balance issues )
- do not alter outer machine taper that goes into the spindle
- with tool installed in the spindle, check trueness of taper that contacts the collet with dial indicator ( should be close to zero TIR )
- if not, consider using the current setup with a boring bar attached to the table to re-machine the collet taper. By design, it should be true to spindle
( collet may seat a little deeper, the only concern would be if the collet "bottoms out" when clamping the smallest diameter that that collet can use )


If an NC, program the spindle to do the taper
- if a manual mill, turn the head to put one side of the taper in a vertical plane ( & use the quill to lower the holder onto the boring tool )
( both methods, check & re-check taper accuracy....if not right, then, the collet will not clamp fully using the entire grip area onto the tool shank )

[taiwanluthiers]

It was both, the runout on the taper within the chuck and the runout on the round bar held in the collet.

The mill's taper is fine, the culprit was the ER chuck arbor. I figured nothing to lose by doing this and was able to fix it.

I don't want to mess with the spindle taper since it already reads close to zero.

[Superman]

It was both, the runout on the taper within the chuck and the runout on the round bar held in the collet.

The mill's taper is fine, the culprit was the ER chuck arbor. I figured nothing to lose by doing this and was able to fix it.

I don't want to mess with the spindle taper since it already reads close to zero.

I think you misunderstood my suggestion

Rework is only on the ER40 holder ( on the collet taper),
Not on the nose cone taper, nor the mating taper on the tool

---, it would be sensible to rework that ER taper in the machine, held by the same method it would be use

[handlewanker]

Hi.....just my opinion, as I have a similar problem with some ISO20 tool shanks with ER32 chucks......some of them have a run out of approx. .12mm.......in the ER chuck collet taper.....spindle is perfect.

I think the manufacture of the chuck is done by grinding the shank down from a common shank size to an ISO 20 body taper or any other taper to fit whatever machine that has the taper required.

This is very difficult to do as there is nothing accurate in that method.

To get the ER taper in the chuck to run true to the shank means you need to run the shank in the spindle and "remachine" the ER taper by a small amount of internal grinding.......this will guarantee the ER taper will run true.......provided the collets are true to both internal cutter bore size and OD of the collet taper.

You cannot hold the tool body accurate enough by running it between centres and regrinding the R8 shank, but you can take out the small amount from the ER chuck bore taper as it's only a few hundredths of a mill.

if you have a cutter grinder.....a rotating head with the R8 taper solves the holding problem, otherwise turning the mill head onto it's side at the half angle, as has been suggested by Superman is the other way and probably the easiest........grinding the ER bore taper is also the best way as it will be too hard to bore it with a boring bar.

Some time ago I used an angle grinder with a long extension adaptor to hold small diam grind stones in a capstan lathe to regrind collets to a larger size........very successfully and accurately too.

When I come to regrind the ER32 chuck bores I'll be using the angle grinder too as it has the speed to run the small grinding stones.

DON'T UNDER ANY CIRCUMSTANCE ATTEMPT TO REGRIND THE R8 TAPER.
Ian.

[109jb]

I disagree with some of what has been said.

First, I will say that no modifications to the R8 taper on the spindle or tool holder should be done UNLESS there is is a problem that can be verified.

The spindle taper can be checked for runout at various distances from the nose with an indicator. If runout exists in the spindle, then investigation as to why should be done. Bearings, wear, poor manufacturing, and I'm sure other things can affect this. Grinding of the spindle taper can be done, but only if all other possibilities have been exhausted. Spindle taper grinding is a relatively common refurb practice, so saying it should never be done is not correct.

If the spindle taper is good, then the R8 taper on the tool holder can be checked. I personally have had tool holders that had a high spot on them that results in pushing the nose of the tool holder off-center when inserted into the spindle. This can be checked by bluing the surface to see where the spindle to tool holder contact really is. Contact should be uniform, but as stated I have had tool holders with high spots that had a smallish area of contact on one side and was corrected by stoning the high spot until good contact was achieved. Why did they have a high spot? Who knows. Maybe the Chinese manufacturer is using a worn out machine to grind them. It doesn't matter why though. This sounds like what taiwanluthiers did, but he should have first blued to check the actual contact surfaces. If a tool holder has a bad contact surface, there isn't any reason that it cannot be fixed one way or another.

The collet taper can then be checked and reground if necessary. Again, no reason this can't be done.

Finally, if all of the above check out and there is still runout, then the collet is probably the culprit

[handlewanker]

Hi....an R8 shank has a straight section at the top and a short sharp taper at the bottom.........if the straight section is loose in the spindle bore it will allow the tool to pivot in the bottom taper from cutter side forces and run eccentric due to the long angle it can throw

It would be a good idea to check that the small pin in the spindle bore is free in the keyway of the R8 tool shank.

If the R8 taper section in the bottom of the spindle is running out then this will also make the cutter run eccentric .......neither of these conditions exist so provided the R8 shank is a good fit in the spindle, it's the ER collet taper in the chuck that has to be rectified.

This is the simplest approach and will make the R8 adaptor run perfectly true......provided the collets also run true.

To re4grind an ER collet that does run out a few microns you would have to mount the collet on a specific diam mandrel for each collet with true centres on each end and then touch up the OD of the collet large end taper with the grinder.

It's not practical to attempt to regrind the ER collet bore as this is a set size, but you can grind the taper on the OD quite easily even in the lathe as it only needs a few microns ground off to make it run true.

There are only a few collets......6...... needed in the full range to hold practically all the standard cutter shank diams from 3mm up to 19mm in the ER32 collet chuck size......even less for the smaller ER chucks.

The other option if you cannot regrind a tool is to only buy high priced known brand tooling that comes with a warranty instead of the bargain basement cheap stuff that has no return to sender option without having to pay the shipping back etc......a poor man always pays twice.
Ian.

[taiwanluthiers]

I already filed a tiny bit off the cone portion of the arbor (not the spindle) and that fixed the problem. I'm not seeing any other issue so I think I'm fine.

[109jb]

Hi....an R8 shank has a straight section at the top and a short sharp taper at the bottom.........if the straight section is loose in the spindle bore it will allow the tool to pivot in the bottom taper from cutter side forces and run eccentric due to the long angle it can throw

Not true. The idea that the tool can pivot in a properly fitting taper, even the R8 taper is ridiculous. Just ask Dave Decaussin, or just watch his video below. On his machine in the video he uses a tool holder that uses an R8 taper with no upper end, only the tapered section is used with a pull stud on top. He was one of the founders of Fadal, so I tend to trust that he knows what he is doing. If there was any merit in the pivot deal, he would not have used an R8 taper for his tool holders.

In this video, at about 8:30 he talks about the "Cat R8" tool holder and shows one. and you can see them cutting too. Proof that you don't need the upper straight portion of an R8 tool to keep the tool running true. The taper can do it just fine.

[taiwanluthiers]

I think the straight part of the R8 shank is to hold the thread. There is no way they are meant to fit exactly in the spindle because if it had zero tolerance it wouldn't fit at all. The taper is what holds it. The shaft requires a little tolerance so that the arbor can be removed, otherwise an arbor press would be required.

[SCzEngrgGroup]

...if the straight section is loose in the spindle bore it will allow the tool to pivot in the bottom taper from cutter side forces and run eccentric due to the long angle it can throw...

The drawbar would have to be little more than finger-tight for that to happen, especially on these small machines that simply can't generate much in the way of lateral force when cutting....

Regards,
Ray L.

[handlewanker]

The problem has been solved so no more to say about it.
Ian.