Am I missing something easier?

Hi everyone,
I've got a c.1928 Brown & Sharpe #2 surface grinder that I've completely rebuilt since it went through a shop fire with the previous owner. All the mechanical bits have been sorted out, and at this point I'm ready to put it into action. Step one is to dress the table top parallel to the long axis.

**BUT** I am unable to lower the spindle enough to get the wheel down to the tabletop. This machine has a pretty lengthy (~12') serpentine belt through a couple of idlers and then a tensioner pulley on the end of a large, heavy arm. As the spindle lowers closer to the table, the belt effectively lengthens, the tensioning arm drops lower and lower, until finally it bottoms out on the base of the machine and the belt slackens.

Seems I have two viable options:
1) make up a shorter belt up that works when the spindle is at the extreme low spot of its travel. I can lace a custom-length narrow belt that's easy enough to get on and off just for this task, but the 'real' belt is a modern, custom-made, permanently joined endless belt, and to take it on and off involves removing the machine spindle. I *THINK* I can arrange the 'good' belt and tie it up in such a way that I can have it clear of all moving parts while the temporary belt is in use for an hour or two cleaning up the table, quite possibly.

2) Machine/3D print some sort of temporary idler/tensioner pulley sheave(s) that increase the ODs and lessen the effective length of the belt. Original belt stays in place, I'm just making a slightly longer pathway for the belt. Depending upon HOW much I need to make up this might or might not work; I'm going out to start measuring up my needed travel to see if it's workable.

Is there anyone here who's tackled a similar situation? Am I missing any obvious 3rd options? Thanks for any and all insights
Mike

Try to make a sleeve that fits over the idler pulley, to increase it's diameter.

trying to get to the top of a magnetic chuck, or to the set pad where the chuck sets?

Agree to find a reason an idler won't travel far enough or add a bigger pulley.

If you can thin and shotten the belt and then glue and stitch it ..that may be an option.

Is that lowest horizontal bar with two idlers able to go lower?

One with belt at limit.

A better title might be
Brown & Sharpe #2 surface grinder belt problem.
Perhaps Eric can fix the title.

Hi Michiganbuck, I'm trying to get to the set pad/top of the table (mag chuck fully removed) in order to get a nice planar and parallel-to-the-ways base for the chuck to sit on. Plan is then to dress the bottom of the chuck, then flip it over and dress the top, once I've got a sturdy base for it to sit upon. My idler arm/counterweight (your picture links) bottoms out on the base of the machine and the belt then slackens when I'm about 1/4" ABOVE the table surface.

I spent some time out in the shop this afternoon evaluating, and the wheel I have on there is worn down to about 6 5/8" diameter. I can (and will, I think) remove the wheel guard (temporarily), put an 8" wheel onto the spindle, and dress it down to about 7.25" diameter. This WILL clear the wheel guard (which I'll reinstall prior to any grinding) on the B&S and allow me to reach the table top.

I'd have to make some fairly beefy sheaves to increase the pulleys enough to make a difference (and I'd be limited with available clearance with all but one pulley), so I think fitting up a slightly-larger than ideal wheel might just do me in this case.

michiganbuck said:

A better title might be
Brown & Sharpe #2 surface grinder belt problem.
Perhaps Eric can fix the title.

Click to expand...

Agreed -- not very helpful to someone searching a similar issue -- good call!

awander said:

Try to make a sleeve that fits over the idler pulley, to increase it's diameter.

Click to expand...

That was my first inclination too, but after looking more closely at the situation, I'm limited in clearance on most of the existing pulleys, and without doing all of the math, would need to add OD to all (or most!) of the pulleys I'll bet and STILL wouldn't be sure it'll be enough....

Grinding a set pad you might first shim up a straight edge parallel zero zero at the ends, and then run an indicator across the bar..reason being if the long travel ways are no longer flat then you won't get a flat grind on the set pad.
Yes, you want the set pad and the chuck bottom flat.

Running an indicator from the wheel head to the set pad doesn't tell the whole story.
I often just check the set pad and the chuck bottom to be flat, and the after a honing put them together.
be sure to one hand elbow swing to tighten the chuck hold downs, about 17 nto 20 lbs is plenty.
Have a 46 k (H through l depending on the wheel brand) or about that, or even a course wheel to wet grind the chuck, white and pink are often better cutting for AO wheels..

Thanks for the advice; I'll definitely plan on laying in a known-good straightedge and measuring if there's any inherent table non-flatness to start. I was also thinking propping up the straightedge on known good 0.250" gauge blocks at each end then measuring with gauge pins every inch or two to get a better view. Is that a reasonably good plan of attack?

Since I'll be grinding in cast; would a silicon carbide wheel be a better bet? I've got a 60J (little finer, but I don't have a 46 on hand) -- will using SC vs. AO make any noticeable difference, do you think?

I suspect your belt is too long. I have the same problem with my #2...I made a belt for it but didn't have an original belt to copy.

When I rebuilt my 1929 B&S no. 2 surface grinder in 1979, I first scraped the ways. I tried it out with the long belt, but was not happy with the surface finish I got. So I bored the bearing tapers out of the head and inserted a motorized spindle that was built for these grinders. The long belt and a lot of pulleys went away and I only kept the belts for the table feed and used a new smaller motor for that function.

The table top should be flat, but it is not essential that it be parallel to the ways if you always use the same 6 x 18 magnetic chuck. After getting the ways scraped, test the table top with a test indicator on the spindle head before you do any grinding on the table to see if it really needs any. If the table and the bottom of the chuck are flat, then you can grind the top of the chuck and it will be parallel to the ways.

Larry

99Panhard said:

I suspect your belt is too long. I have the same problem with my #2...I made a belt for it but didn't have an original belt to copy.

Click to expand...

It is not impossible to shorten a belt, There are You tubes on that subject and very glue. with a too log belt that may go in the trash, it might be worth a try.

Perhaps try 1/4" (or what) thick something added to the small swing arm pulley.
Seems adding 1/4" would shorten the belt over 1"