Main Table and Trunnion Alignment Before Mounting

[dusty]

After watching Jim McCann discussing Main Table Alignment prior to the Table Assembly being installed on the Shopsmith I was prompted to resurrect this jig approach. I gave up on this back when I was striving for alignment accuracy to within .003". In one of the videos it is stated that the factory now alignes to within .010" over 10".

I think this can be done with a block of wood.

Main Table Alignment Footprint.jpg (102.67 KiB) Viewed 1651 times

Main Table Alignment Foorprint with Jig.jpg (68.38 KiB) Viewed 1645 times

[DLB]

After watching Jim McCann discussing Main Table Alignment prior to the Table Assembly being installed on the Shopsmith I was prompted to resurrect this jig approach. I gave up on this back when I was striving for alignment accuracy to within .003". In one of the videos it is stated that the factory now alignes to within .010" over 10".

I think this can be done with a block of wood.

I've assumed that the interface between the table and trunnions allows us to offset for errors elsewhere in the system. Examples of those errors being primarily manufacturing variation and wear. Aligning it with a jig like this would seem to assume that the only errors you need to adjust for relate to the table and trunnions themselves. Whether it works or not may depend on what results you consider acceptable. We know, based on the $20 bill trick, that an error of only a few thou may cause binding of the table tilt. And an error in the other direction will cause the table to flex under the load of the locks. That's pretty sensitive and does not include the angular adjustment of the table.

I've seen a few variations on the 'book' alignment procedure. I suspect that none of them would reliably produce results better than .010" over 10 inches. Hard to say for sure, as they don't include quantified measurements. I try to stay within 0.005" over about 6-1/2" of usable saw blade surface. That's not much different than the factory number, though it sounds better.

- David

[dusty]

After watching Jim McCann discussing Main Table Alignment prior to the Table Assembly being installed on the Shopsmith I was prompted to resurrect this jig approach. I gave up on this back when I was striving for alignment accuracy to within .003". In one of the videos it is stated that the factory now alignes to within .010" over 10".

I think this can be done with a block of wood.

I've assumed that the interface between the table and trunnions allows us to offset for errors elsewhere in the system. Examples of those errors being primarily manufacturing variation and wear. Aligning it with a jig like this would seem to assume that the only errors you need to adjust for relate to the table and trunnions themselves. Whether it works or not may depend on what results you consider acceptable. We know, based on the $20 bill trick, that an error of only a few thou may cause binding of the table tilt. And an error in the other direction will cause the table to flex under the load of the locks. That's pretty sensitive and does not include the angular adjustment of the table.

I've seen a few variations on the 'book' alignment procedure. I suspect that none of them would reliably produce results better than .010" over 10 inches. Hard to say for sure, as they don't include quantified measurements. I try to stay within 0.005" over about 6-1/2" of usable saw blade surface. That's not much different than the factory number, though it sounds better.

- David

Even though I have years of experience with my two machines, I don't understand what wear and tear you might anticipate that would cause the table to go out of alignment. This said with the assumption that we are not anticipating abuse or misuse.

The entire community seems to accept the process of loosening the trunnions and adjusting the table to the blade. Jim implied that this procedure is done in the factory during assembly of the table system (table tie bar, trunnions and table) using a factory alignment tool (jig). If it can be done that way in the factory (without reference to the blade) I see no reason why it can not be done by you or I on the bench.

Align the trunnions to the table.

[jsburger]

I wonder what the reference surface is for the factory alignment jig. Scott said Jim would not let him take a picture of the jig when he toured the factory.

[dusty]

I wonder what the reference surface is for the factory alignment jig. Scott said Jim would not let him take a picture of the jig when he toured the factory.

If the table alignment is completed (in the factory) before the table is mounted on a Shopsmith I would bet that the reference surface is the plane formed by the edge of the table legs. That is the only possible "reference surface" that is parallel to the blade (after assembly).

The inside face of the trunnions (on an aligned table) would be perpendicular to the plane formed by the blade and could be used but the table position would have to be controlled.

With the suggested procedure I used to start this thread it is assumed (yes, assumed) that the table legs are in a plane parallel to the plane of the blade.

I'll report on this once I have my machine back in condition where I can make two or three very precise cuts (required to produce the referenced jig).

I think this is a slam dunk on the table I have but I don't know if all of the main tables are built with the same rib structure as mine. I have four tables representing at least two different vintages (505/510/520 only).

[jsburger]

Does that not mean the holes in the carriage are parallel to the blade?

Another thing I found interesting in the interview was when Jim was talking about stuffing the Power Pro inside existing head stock castings. He said they have numerous head stock castings from the earliest 'A' sand castings. He said what he found interesting that Magna and the other owners kept the internal mating surfaces very close to the same over the years. To about 0.012". He said it made it easier to make sure the Power Pro conversion would fit in any head stock.

[dusty]

YES. Tie a string across the table legs and see for yourself. Something other than a string will be required if you want to determine tolerances.

[jsburger]

But, parallelism of the tubes is the result not the reference. There has to be a reference 'surface' on the table to achieve that.

Then we introduce the bores in the carriage for the way tubes that effect the parallelism of the table bores in the carriage. It seems to me when you stack all the variables up they individually have to be very tight to get 0.010 over 10" with a jig.

[JPG]

The purpose of the table adjustment is to align the miter gauge slots to the blade.

ANY reference surface parallel to the slots will do. Edge of the table?

Now what is adjusted other than the trunion location. Where is the 'reference' there.

IIWM, I would have the jig reference the miter slots and the trunions. That establishes the miter gauge slot to the trunions. Kicker is where on the trunions?


I wonder if the table is in 'normal' position or 'raised' position? If the latter, slot normal to tubes will get r done.

[dusty]

The simple block of wood in my two images captures the two trunnions and a rib on the under side of the table. Holding that position while securing the trunnion bolts is what completes the table positioning. The miter slots in m,y two tables have been verified to be parallel to one another AND are parallel to the rib on the table. That is the reference for adjustment.

Everything else is dependent on the inherent accuracy of the remaining assembly.

Jim has stated that the factory alignment of the table is now completed prior to it having been mounted (onto the carriage) my words NOT Jim's. If I read that right this will work.

I've played with this and other similar methods for years and I no longer believe that the dial indicator (.003") solution is the only way to achieve what we need.

Shopsmith will never buy into this and I understand that. There are too many legal applications.

Others will not buy into this believing that the stacking of tolerances makes it impossible and I understand that.

I lived a goodly part of my life as a quality production engineer in a manufacturing facility with the DoD as our customer. I am equally convinced that it can and will work. Time will tell. Unfortunately I no longer do the amount of work in the shop to validate the theory quickly.

Cutting a few pieces of wood with no burn marks, no saw tooth marks, no binding and easy to achieve 22.5 degree cuts will be my checkered flag.