grinding a mill spindle

[freddycougar]

what kind out outcome would a router, with a point mounted in it... used to grind a internal taper??

i have a millrite with a r8 taper.. it indicates 002 run out, with a collet and a endmill.. i have tried differet collets .. same reading.. i also indicated the actual taper ..same results..this is after i cleaned and relubed the bearings.. and adjusted the preload... readings were the same. so i am thinking of grinding the taper..

is this gonna work or is this just a bad dream?

freddy

[Mcgyver]

freddy sounds like a bad dream to me - I wouldn't try it based on the bearings in a router not being up the to standard of those in a grinding spindle.

could it be an isolated bruise or dimple, then again you say you indicated the taper so that can't be it. it seems strange that the whole thing is that far out -they look like a decent machine, american made, short of bent spindle, why's it so far out? if you've had the spindle out can you set it up on the lathe and try to figure out where the error is?

i don't know what the spindle rebuilding places charge, but it would be worth at least knowing before you decided to go at it. next best would a lathe with an internal tool post grinder and taper attachment.

[freddycougar]

hu..?

the bearings are tight in a router.. thigter than a pencil grinder.. i was thinking.. that i would clamp the router down on the table ,,point up.. tilt the head so that the taper would indicate .00 and rase the knee till the out of round was gone.. what u think?
freddy

[Mcgyver]

beg borrow or steal an internal grinder, ie tool post or attachment from a T&C grinder and it might be worth a go. axis of the two spindles must be perfectly in the same plane. there was a thread on cnczone awhile ago along the same lines, but using the x/z motion to interpolate the angle, actually there is a professional co. doing this this way for cnc machines. general consensus was that the bearings in router or dremel weren't up to the task, imo that's why a router is $100 and a dumore spindle is $2000.

still, before I'd remove material from a component as expensive and crucial as a spindle I'd be 1) trying to figure exactly where the error lay (ie indicator, lathe, steady rest (now that you've made one ) , and 2) pricing out spindle repair services.

just my $0.02, I'm by no means a spindle expert, I'm sure they'll chirp in at any moment...

[A.K. Boomer]

I third that, find out for sure what went down, it wasnt built that way and let out of the factory, they wouldnt let something like that go on the most bottom line pieces of crap,,,,, so you either got a high spot or a bend, maybe the machine got crashed, but i would never attemp a grind if i were interested in getting factory close....

[freddycougar]

ok..

i want to grind the spindle in its own bearings..i am sure what ever i do will reduce the run out
like 001 of metal removed.. i am out in the sticks so one way or the other this is gonna happen.. just wanted some pointers<<<<>>>>\ just say it can b done and if i have too i wil build a TPgrinder....but i am more stuburn than a dead jackass
freddy

[A.K. Boomer]

i want to grind the spindle in its own bearings..i am sure what ever i do will reduce the run out
like 001 of metal removed.. i am out in the sticks so one way or the other this is gonna happen.. just wanted some pointers<<<<>>>>\ just say it can b done and if i have too i wil build a TPgrinder....but i am more stuburn than a dead jackass
freddy

Oh god,,, i know theres no talking to you because im the same way, question, how do you plan on keeping the correct taper throughout?
also, what if the machine crashed and it indented the outer bearing race into its mount or cocked it, then you grind the spindle (which was true) get a little use out of it but the spindle bearings trash early because they seen trauma, you replace the bearings and then because you took care of the real problem now your back out to .002 thou off because your spindle is ground wrong,,,,,,,,,, rule #1 varify where the problem is before makeing any "life altering changes" just my two cents good luck with it.

[freddycougar]

ok i

forgot to mention.. i indicated the od of the spindle.. pretty well .00 it was a bit roughed up .. but not 002 out
freddy

[Randy]

Maybe I just like to live dangerously, but I think your plan is just fine. I've considered doing the same thing using my homemede tool post grinder, but my mill's spindle isn't bad enough to require regrinding. Your router's bearings might be good enough, any deficiency would show up in surface smoothness, you sure won't make the spindle out-of-round or more off center. You might have to do some polishing. And anyway, sticky collets are preferable to ones that run out. You'll want to advance the table only a few tenths between grinding passes, and I wouldn't trust the hand cranks and graduated collars to work that finely. I'd monitor the table position with a dial indicator. Preferably one that reads in tenths if you have one, but I wouldn't run out and buy one just for this job. And I'd move the table with a couple of taps from a deadblow hammer. You'll also want to be sure the gibs in the knee are pretty snug so that it doesn't swing from side to side as you crank it up. If you work carefully I'd bet that you can get a good result, with very little chance of making things worse.

[John Stevenson]

OK Freddie so you are out in the sticks and I'm going to get some for this post

Read all the relevant points about your spindle. It doesn't seem bent or the runout on the OD would match the taper.

First thing is the head needs to be trammed dead on in both planes.
Then you have to work out just were the problem lies.
There are two critical dimensions on a R8 taper. The top register at 0.949 to 0.9495 and the taper, which is 16 degrees 51 minutes.

To check the top register take a 1" bar about a foot long and turn a diameter of 0.9495 on if for about 1", then reduce this to just under [ not critical] for about 4".
Take this bar and mount it in a chuck bolted to the bed, turned part upwards and enter this into the top spindle register.
Place a dial gauge just clear of the taper, run the machine in low speed and watch the gauge.
If the register is OK you have no problem there, if you have run out then you have serious problems and grinding will only make it worse.

We'll assume that this is OK and move onto the taper.
You know you have problems there as you have indicated them.
Two thou isn't that much, it's actually a thou a side.

Now for the flack, asbestos suit on

Tale a stub of steel about 1.5" diameter by 2" long and weld a square plate about 5 to 6" onto one end, The plate want's to be decent about 3/8" to 1/2" thick.
Then spin this and face the plate up so it's flat.
Drill 4 holes in the corner to match the machines Tee slots and using these bolt it to the faceplate of the lathe.
Now you have to turn a taper on it to match the spindle taper.
As long as the large end is greater then 1.250" and the taper is correct that all that matters, polish to a good finish.

Now bolt this to the bed of the machine, and centre it onto the spindle.
LOCK THE BED.

Now using covers on the bed and a smear of grinding paste, using low speed take the bed up to just lick the spindle.
Drop down and check where it's rubbing.
This should show up the error visibly. using blue or a felt tip pen mark the spindle and take another light cut to see the result.

It won't take much to remove a thou by this method.

Needless to say clean up well afterwards.

Now I know this routine will upset some people but it works, I have seen 8 to 10 thou removed from horizontal milling spindles this way after crashes.

.

[Evan]

Here's a reference drawing. Don't remember where I found it, might have been while snooping around John's files

[John Stevenson]

No problem with that Evan, They are not locked in any way.
What's there is free for anyone to look.

Here's the links

http://homepage.ntlworld.com/stevenson.engineers/lsteve/files

and

http://homepage.ntlworld.com/stevenson.engineers/lsteve/hidden/

Really want's renaming as they are not hidden.

.

[freddycougar]

thats the ticket...

very informative john.... i will try it!!! thank you, and thank all of the othe members who replied on this post it was very good info... its true u can skin a cat 9 different ways..
thanks again
freddy

[Forrest Addy]

I've ground many a spindle with a dressed mounted wheel in a die grinder. The tricks are a good set of ways to mount the grinder on and to get the center of the wheel (and the dresser) on the radial plane of the taper.

First you have to determine a few things.

- One is does the collet index screw affect the collet's draw?

- Another is have you dialed in the small end (straight bore) of the collet?

- Is the straight bore a good fit? (collet size to plus 0.0005") If the straight upper collet bore is in bad condition there's really nothing you can do to fix it except sleeve it with a little skinny wall sleeve and that takes the most excruciating care to install and bore correctly.

Since this is a turret mill you can incline the head to the collet taper half angle and mount the grinder to anything convenient that's rigid. If the table ways are in acceptable condition these will serve to guide the grinder.

Dress the wheel with a collet mounted dresser made of a bent 5/8 dia rod that locates the diamond in line with the collete taper.

Control the depth of cut with the knee and a "tenths" indicator to register movement.

Make a good plan, protect the machine from fly abrasive, get the taper right (use a new shell mill arbor to gage with), and procede with care.

It a job that requires care but it goes well enough.