I did a home brew belt conversion several months ago based on the Hoss Machine article and drawings. It has been a great improvement, particularly the high speed increase from stock and I am pleased to say I have had no issues and no overheating.
The bearings should not be getting so hot and I suspect that the pre-load is far too high. Has they always run so hot or did you overdo the adjustment on reassembly? Often the spindle is a little too large which does not permit the inner race to move smoothly when the preload is increased and it will then give suddenly showing a sudden decrease in the play but a large increase in the drag which shows as a hot bearing. The increased drag also leads to a large increase increase in the motor temperature whuch is not a good thing. I would suggest loosening off and then re-setting the pre;load. Initial small adjustment should lead to a quite rapid fall in play with little increase in temperature and the reduction in play will become less for the same adjustment and the temperature increase will become noticeable and ultimately you will get little or no improvement in play and an overheating bearing and overloaded motor.you need to aim for the sweet spot of minimum play consistent with the bearings stabilising after time to comfortably warm to the touch.
I achieved this fairly easily with the stock bearings (which are sealed bearings), if you cannot it may be that you need to swap out the bearings for better ones. Many people correct any spindle oversize at the same time which makes adjusting preload easier.
The motor is configured to draw air up through the bottom bell and discharging through the top. The stock Boss design has a large central hole providing clear airflow. I am running a 1.67" pulley with a 2.25" hole and that is adequate, my motor never runs more than warm.. It is possible that if you are running a larger pulley to get the higher top speed that this is blocking a portion of the airflow and driving a corresponding increase in temperature.
Hopefully readjusting the spindle bearins will lead to a considerable fall in the motor temp but if not I would suggest modifying the new motor plate clearance hole by putting a 45 deg or so chamfer to effectively increase the diameter and reducing the blanking effect of the larger hi-speed pulley. there is plenty of meat in the plate to allow this without affecting strength. It may also be possible to modify the pulley from solid to spoked by drilling clearance holes through the outer pulley again reducing the blanking effect of the larger solid pulley as you yourself mentioned.
Hope this gives you some ideas.
Gerry
Leeds UK
________________________________
> To: GrizHFMinimill@yahoogroups.com
> From: c_reynolds2571@yahoo.com
> Date: Mon, 7 Nov 2011 14:44:50 +0000
> Subject: [GrizHFMinimill] Re: how hot
>
>
>
> I recently put a belt drive conversion on my X2 as well and ever since
> then it has run really hot. The pulleys that I made were based on the
> HossMachine.info conversion and if I let it run at full speed on the
> high speed pulley the spindle head of the mill will get up to 130
> degrees and the motor will get up to 120. That can't be good for it.
> Before the belt conversion I would consistently run the mill at full
> speed and I don't ever remember the motor getting hot like that.
>
> Does anyone know if there are any better upgrade bearings I can put in
> the spindle head and motor so that I can use the 6000rpm capability of
> the belt drive without the head getting that hot?
>
> I thought about taking out the bearings, cleaning, and repacking them,
> but they appear to be sealed bearings. Something else that I noticed is
> that after the belt conversion the motor doesn't seem to draw in as
> much air as it used to, which I think is the main contributor to the
> heat issue. When I put the smaller of the two pulleys that I made on
> the motor it runs cooler, most likely because there is more room around
> the pulley for air to be pulled into the motor. It got me to wondering
> if it would be possible to make another pulley with a series of holes
> drilled through it, that would help draw air and force it into the
> motor.
>
> Chris
>
> > Jeff, an old "Bull of the Woods" machinist pointed this out to me years
> > back. He would walk through the shop and lightly touch each motor on
> > machines in use. If he could leave his hand on the motor then it was not
> > working hard and neither was the machinist! Motors are (were) rated to
> > run at 30 degrees above ambient. In a 68 degree shop that's a warm 98
> > degrees and in a 90 degree shop (like I recall!) that's 120 and quite
> > warm to the touch!
> > So if you are working your little motor hard then it should be warm to
> > the touch. A non contacting thermometer (~$20 at HF) will tell you
> > exactly how hot your motor is and also where the heat/cool is going in
> > your house too!
> > With luck there is a nameplate on your motor that will give the power
> > rating in watts and the temperature rise above ambient! Bill
> >
>
>
>
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