Bandsaw Table Installation and Alignment

[dusty]

There are variations in the Trunnions or at least how they mount between the newer Bandsaws and the older ones. I am not sure about the Trunnions themselves but the parts used to mount them to the Bandsaw's Main Frame (back) is different. This is where one of the changes in the Main Frame assembly occurred. The earlier Bandsaws have pressed in sleeves with "V"s in the ends which has been changed to slip in sleeves with smooth ends for newer/current Main Frames. Other hardware there has changed to match. I'll try to check the actual trunnions between the 1956 and the 1998 Bandsaws when I remove the tables to check for shim washers discussed before. If the Trunnions are different at all they must be very close or at least have the same mounting spacing to allow upgrading to the aluminum table from the cast iron table without including new trunnions. I am not sure when the Main Frame assembly changed but a Bandsaw made in December 1985 had the pressed in sleeved and a February 1996 has the slip in sleeves. This is a close as I can come for this change based on Bandsaws I have seen/owned.

I doubt that you can tell much from this but it is the most telling of the trunnion pictures taken when I had the table off.

20210308_072651.jpg (347.39 KiB) Viewed 875 times

[chapmanruss]

I went through the 1956 and 1998 Bandsaws today. First the trunnions are almost the same. The only difference between them besides the 1956 trunnions not having the black coating is the tabs where they bolt to the table have around 45° cut off corners (see picture below) whereas the newer ones look like the ones in Dusty's picture above.

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picture from another source

Bandsaw Cast Iron Table Trunnions.jpg (119.48 KiB) Viewed 833 times

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I had previously setup both of these Bandsaws with the blade at 90° to the table. They are going to remain that way at least for the time being. I guess I'll keep the 2006 Bandsaw with the 2° cant for now. I can always sell it later.

Thanks again Dusty for prompting to spend some time with my Bandsaws.

[chapmanruss]

As I have been re-reading this thread and information I have read plus things I have seen on the Bandsaw itself has me wanting to make some corrections to some of my previous statements.

garys, said

I believe there was also a change in the bandsaw itself. Didn't the earlier versions have the wheels aligned straight with each other? And, aren't the newer ones set up with the top wheel tilted a few degrees? Perhaps changes in the saw itself caused Shopsmith to suggest different setup.

paulrussell had said this,

Unless I am terribly mistaken, all Shopsmith (Magna) bandsaws have utilized the same canted upper wheel with tracking bearing.

I followed that by quoting this,

Upper Wheel angle - From Everett January 15 2016 in a forum post.

I just got off the phone with Shopsmith Customer Service and was told that the 2° Bevel was added in April 1984 to the upper wheel. Prior to that, they said they were flat like the lower wheel. That may answer some of the questions since many of us have Bandsaws from early and later production.

Now here is what I have learned since. paulrussell was correct. I already knew my 1956 Bandsaw has a canted wheel and now I know in reading the patent application for the Bandsaw this was part of the original design. The designers/engineers wanted to make a Bandsaw that was easier to setup and use. They wanted blade changes to be simpler without the need to realign pretty much everything when changing blade widths. Bandsaws at the time (1950's) required more steps to change from a 1/2" blade to a 1/8" blade for tracking. Another feature was a single lever to adjust the upper blade guide height to keep it closer to the material being cut and not needing so many separate adjustments. The following is from the 1982 Manual in the alignment section. Other manuals have it worded differently but the end result is the same.

The back of the blade should rest against the auto-track roller and the lower blade guide roller, and should be no more than 1/64” away from the upper blade guide roller.

I have to look further to find out why the blade has the slight cant to the table as we have discussed throughout this thread.

[edma194]

I finished some upgrade work to my bandsaw, tension gauge window, hole for the tension wrench, dust collector port, and Carter guides. I finished up by removing and cleaning the table and trunnions. It's never been shimmed and was always perpendicular to the blade, or very nearly so. I don't know how that was the case without shims. In finishing it up I got the blade absolutely perpendicular to the table with the addition of just one soda can shim on each side of the front trunnion ends. Perhaps the previous owner adjusted the backup bearings somehow, the upper wheel seems to have the slight angle. This saw is serial number 135408, don't know how old that is.

I have two older bandsaws, 113956 and 75210, someday I'll check those out. Neither has any shim washers right now.

[JPG]

Since the patent drawings show both wheels with a 2° cant(s/b bevel), I believe the 1984 SS quote is simply inaccurate. Perhaps someone did not read the patent drawings before 1984?

Those patent drawings also explain the blade not being perpendicular to the table. I think we can assume the table top is in line with the drive shaft.

That being so, the lower wheel 2° bevel forces the blade to slant back at that 2° angle(s/b 0.625°). Now the blade must also mate to the upper wheel bevel as well, but that requires the upper wheel to be canted. IIRC that cant angle is 4°(s/b 1.25°).

[dusty]

Since the patent drawings show both wheels with a 2° cant, I believe the 1984 SS quote is simply inaccurate. Perhaps someone did not read the patent drawings before 1984?

Those patent drawings also explain the blade not being perpendicular to the table. I think we can assume the table top is in line with the drive shaft.

That being so, the lower wheel 2° bevel forces the blade to slant back at that 2° angle. Now the blade must also mate to the upper wheel bevel as well, but that requires the upper wheel to be canted. IIRC that cant angle is 4°.

SEE ORIGINAL POST FOR CORRECTIONS

The combination of bevels and cant do cause the blade to drift back until it contacts the backup bearing(s) but I do not buy into the conclusion that the blade also tilts because of that. The blades are pretty rigid.

You read more into the patent than I do but that is OKAY. During the time I spent as an Engineer's Technician I hardly ever was in full agreement with the engineer.

[edma194]

I doubt that you can tell much from this but it is the most telling of the trunnion pictures taken when I had the table off.

20210308_072651.jpg

Referring to that picture, those look like common washers. Were they shims supplied with the bandsaw? If I put something as thick as those on the front trunnion the blade would be angled far forward at the top. Next blade change I'll have to get in with a straight edge and check the alignment of the backup bearings to each other and see if I can compare that to the wheels. I'm also finding the explanation of the tilt to be off some how.

JPG, I'm not clear what you are describing about the lower wheel bevel. Is it the shape of the tire track that is beveled to have the blade drift toward the backup bearing?

[dusty]

I doubt that you can tell much from this but it is the most telling of the trunnion pictures taken when I had the table off.

20210308_072651.jpg

Referring to that picture, those look like common washers. Were they shims supplied with the bandsaw? If I put something as thick as those on the front trunnion the blade would be angled far forward at the top. Next blade change I'll have to get in with a straight edge and check the alignment of the backup bearings to each other and see if I can compare that to the wheels. I'm also finding the explanation of the tilt to be off some how.

JPG, I'm not clear what you are describing about the lower wheel bevel. Is it the shape of the tire track that is beveled to have the blade drift toward the backup bearing?

What you see in that photo are common washers and I used common washers (not those) when I did the table installation. I used a combination of common washers and shims for the final table installation. Yes, the table tilt without the washers was quite significant. I DO NOT believe that my table and trunnions should be used as a reference to what ir correct. I believe mine to be atypical.
With regard to the tilt explanation...what doesn't settle well?

[JPG]

Both wheels are 'beveled'. The od of the wheel on the side closest to the base is greater than the od of the wheel at the open side.

The upper portion of the blade laying flat on that bevel on the lower wheel will tilt away from the open side.

[edma194]

With regard to the tilt explanation...what doesn't settle well?

I guess I'm just missing some piece of info. The upper wheel cant should have the blade drift toward the upper back up bearing. My assumption was the lower wheel was vertical and positioned relative to the upper wheel to keep the blade in position, but I had never really tried to work that out. So it seems like the backup bearings should be offset so the blade is following the 2 degree cant from the top wheel, but then must be drifting back after passing the lower backup bearing onto the vertically aligned lower wheel. And perhaps it is only that change in angle from the cant of the blade to the vertical wheel that puts the backward pressure on the blade. Maybe that's what everyone is saying here and I just didn't pick it up.