drawbar tightening- how hard?

After having to use a copper mallet to extract a 2mt fitting from it. I wonder how hard should one tighten a mill drawbar? After all it's only to stop the fitting being pulled out by the action of the cutter ? vibtration from intermittant cutting isn't it?

If that displays my ignorance please forgive me. It's just reading the recent MEW about an extractor that made me question how tight I need to have the drawbar in the first place? Currently I make damn sure it's tight using a spanner ( 6 inch long spanner) but this is operating a 10mm square bolt head. Perhaps if I wasd a little less enthusiastic with the spanner??

Thoughts please?

"not very" it's job is to stop the taper vibrating loose, not to 'lock' it in place. MT tapers are 'self locking and driving, so I literally just wind it up hand tight then put a little nip with a spanner.

Neil

Neil has answered your question very well. As an extra on exactly why you shouldn't over tighten that drawbar. Hard hammering on the end of the drawbar will drasicly shorten the life of your spindle bearings. There's not a ball or roller type bearing made that will tolerate high shock loads to them without shortening that life span.

Pete

I pull mine up pretty hard (Emco FB2 clone with 2MT spindle), but the machine has a captive drawbar so it also jacks the tool out with no hammering required. The spindle nose has two flats & the machine was supplied with a spanner to suit - the drawbar has a 6mm AF hexagon socket. The two combined offer a good grip to tighten or release the drawbar without stressing the bearings.

I made a face mill holder that, when inserted by hand, is around 2 thou clear of the spindle nose - tightening the drawbar brings the back face of the holder into firm contact with the end of the spindle nose. This is similar in principle to HSK or Capto tooling & makes for a stiffer connection, but also requires a good pull on the drawbar to accomplish..

I have not had any problems with tooling coming adrift in operation - likewise no problems extracting tooling after use, though it sometimes releases with a bit of a crack !

I also have an RF30 mill drill (3 MT taper) that has yet to be used in anger. That will require the drawbar to be made captive to remove the need to pound on the bearings while removing tooling.

Nigel B.

A little nip with spanner guaranteed to slip but ok for drills thats about it.

Tighten the things and be done with it, dont want the cutters dropping. Been there nipped up and forgotten, later usage seeing the job scrapped due to cutter dropping.

As regards bearings, the chinese use the poorest bearings available. In saying that the larger mill used daily probably sees more use in a day than a hobbier in 12 months, has lasted 7 years on originals. Good quality SKF were only £30 ish last year.

Bearings still good on the RF25 after 5 yrs hard labour.

Be careful not to place a cold morse taper into a warm spindle. Its expansion will make it a very firm fit.

Good quality SKF were only £30 ish last year.

They may be "good quality", but I doubt that they were precison (P6, P5 or P4) at that price.

And there is a very good chance that the "quality" brand was made in China as well.

Many thanks for advice . I must admit I have probably overdone it. The mill has a captive drawbar but the tooling was able to not totally disengage when extracting. The adaptor that holds it is just engaged about 1 1/2 turns, needs a longer adaptor- another job!

Especially thanks for advice re bearings, don't want to have to replace!

Regards Ian

on my 3mt arbors i have a draw bar with a 30mm knurled top and this is sufficient for everthing i do (just hand tight)

james

Well tried less tight and span a 3MT today so maybe a bit tighter than hand tight next time. No damage to 3MT or to new 4mm woodruff cutter- phew!

Ian

Don't forget the 'nip' with the spanner

Neil

Neil

I didn't forget but tried a quarter turn, next time it's a full half turn ! But it saved the cutter edge I believe so overall OK.

Thanks Ian

PS Not long to Harrogate !!!!

As Stub Mandrel advises, you need just a little nip with a spanner to tighten it. You ain't using a 4ft crowbar !

Dennis