Should the drawbar be centered in the spindle?

M

michkhol

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Hi folks,

I'm new to this forum but have been watching it for some time. I've jut got a G0619 milling machine and am trying to get it running. I noticed that the top of the drawbar always gets off-center when I tighten it up so it brushes against the spindle cap and makes loud noise. I can see from various pictures on the Internet that sometimes the drawbar has a flange or a flange washer to keep it centered in the spindle. There was no washer supplied with this particular drawbar. It has a flange, but the diameter of the bar below the flange is bigger than the spindle ID so it does not go into the spindle but sits on top of it. I wonder if it's a wrong drawbar or notorious chinese quality or it's pretty normal to have the drawbar off-centered. Any advice would be appreciated.

Mike
 
Drawbar should be centered. Can you turn it down to fit? Mostly, I have seen drawbars smaller than the hole, and they have a shouldered bushing to center them. Sounds like you have the opposite problem.
 
Thanks, Tony!

Yes the problem is that the bushing is larger than the spindle ID. The obvious solution is to turn it down but I don't have the lathe yet. (This is my next project :) Anyway, how snug should it be?
 
That end of the mill is not the "precision" end, so no need to strive for a very close fit. 0.005/0.0010 is loose enough not to give fitup problems, and still be plenty close to keep the drawbar centered. You don't need a long shoulder turned on it either. 1/4" will do. That way you aren't changing the thread engagement on the collet/toolholder end enough to cause problems most of the time. If it does, simply shorten the threaded end the same amount as the shoulder you added. Watch that you don't run out of thread though. Some drawbars have just enough thread to make up, with very little excess thread length.
 
Just a sliding fit is fine. You don't want an off center drawbar vibrating your spindle. It isn't the best thing for the bearings,and could affect the quality of the surfaces you mill because of vibration.

You could use the mill as a lathe,perhaps. Use a large R8 collet to hold the bar of metal,and bring the metal down past the vise,in which is clamped a lathe bit sticking out of 1 side. Move the bar of metal slowly down past the lathe tool to reduce it to the required diameter. You should accurately measure the inside diameter of your spindle hole at the top,where the draw bar is wobbling. You could turn the bar of steel to be a snug fit in the hole,and leave a flange of larger diameter at its top. Cut the plug off using the mill,or just saw it off as squarely as you can. Then,as carefully as possible,drill a hole that the draw bar will pass through with minimal clearance. Center it carefully as possible. When finished,push the plug into the top of the spindle. The flange will keep it from dropping down into the hole.

Or,can you just shorten the draw bar some,and add threads where you cut it off so that it goes into the hole as it should?
 
Thank you for your help, guys! I'm more inclined to find a lathe and turn it down, because first I'm not sure it would fit under the spindle cap with the plug inserted and second I'm reluctant to use the mill at all with this issue. I contacted Grizzly and they sent me the drawbar which is supposed to be the right one. Personally I'm skeptical but at least I will have a spare drawbar to play with.
 
Ok, finally I did it. First, the drawbar could not be turned down because the locking pin on the bushing was too close to the edge. So I opted for the flanged thrust washer which fit nicely. The advantage is, I can use any drawbar with it. The drawbar does not wobble anymore, I only wish the cap hole was centered relative to the spindle (ubiquitous chinese quality).
 
I found this thread very interesting as I am going to be attempting a manufacturing of a draw bar for the 10L. Always looking for tips and ideas! Thanks.
 
drawbar

i made my drawbar out of a 3/4 gas pipe and machines me a bronze step collar to slide into the spindle, it worked great for me:biggrin:Mac
 
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