Are My Trunnions Mounted Correctly

dusty · Post by **dusty** » Wed Aug 13, 2014 6:39 pm

This thread is being started as a separate discussion but is directly related to the "Drill Bit Not Square to the Table" thread.

Assuming that my Main Table is flat (at least to within Shopsmith specifications), what could cause (or allow) the table to be twisted out-of-tolerance when the trunnion bolts are tightened?

Each of the two trunnions is secured to the bottom of the table with two bolts. These bolts pull the trunnions tight against two threaded platforms cast into the bottom of the Main Table.

If those platforms are not of equal height, the trunnions would simply be secured to them and their plane would not be parallel to the plane of the Main Table. I don't think that this would cause the Main Table to twist. Remember, the trunnions swivel on an "axle like" element of the table

The same goes for the trunnions. If the top surface of the trunnions was not flat the same scenario would occur.

I'm thick. I am having a hard time seeing how tightening the trunnion bolts can be the cause of this issue.

wa2crk · Post by **wa2crk** » Wed Aug 13, 2014 7:03 pm

Is the tie bar between the trunnions bent? Didja drop the table assembly at any time in the past and maybe bent one of the mounting tubes? Have you checked the mounting post assembly and or the carriage for things out of square?
Bill V

beatnik · Post by **beatnik** » Wed Aug 13, 2014 7:24 pm

Can you take them off and set them on something cast and flat to check their not twisted, bowed or something ?

beeg · Post by **beeg** » Wed Aug 13, 2014 7:50 pm

dusty wrote:I am having a hard time seeing how tightening the trunnion bolts can be the cause of this issue.

I can see that issue. Are the bolts tightened EVENLY.

dusty · Post by **dusty** » Wed Aug 13, 2014 8:02 pm

beatnik wrote:Can you take them off and set them on something cast and flat to check their not twisted, bowed or something ?

I have two sets of trunnions off. They do not appear to be twisted or bent or in any other way deformed. But have you looked at the trunnions? Those are a pretty stout chunk of cast.

dusty · Post by **dusty** » Wed Aug 13, 2014 8:04 pm

wa2crk wrote:Is the tie bar between the trunnions bent? Didja drop the table assembly at any time in the past and maybe bent one of the mounting tubes? Have you checked the mounting post assembly and or the carriage for things out of square?
Bill V

Good questions but I don't know how to verify most of what you are suggesting.

I can say that the tubes slide up and down in the carriage with no problem.

dusty · Post by **dusty** » Wed Aug 13, 2014 8:06 pm

beeg wrote:I can see that issue. Are the bolts tightened EVENLY.

I don't torque the trunnion bolts. Do you? I just snug them down tight. Maybe they should be torqued but it doesn't say to in the instruction manual.

algale · Post by **algale** » Wed Aug 13, 2014 8:07 pm

dusty wrote:I have two sets of trunnions off. They do not appear to be twisted or bent or in any other way deformed. But have you looked at the trunnions? Those are a pretty stout chunk of cast.

Does the table change its shape when you mount the trunnions to the table without the trunnions themselves being mounted to the pins/axles?

wa2crk · Post by **wa2crk** » Wed Aug 13, 2014 10:38 pm

Dusty
Can you just put the table on the trunnions and without tightening the bolts see if you can rock the table corner to corner? If you can, then the trunnions are not true to each other. O the table is in fact warped You might also try to remove the table from the trunnions and put the assembly, (without the table attached ) on a known flat surface like a piece of MDF and see if the trunnions rock or stay true to the surface.
The first thing to determine is which piece is the offensive one.
Bill V

JPG · Post by **JPG** » Thu Aug 14, 2014 12:10 am

If the 4 mounting bosses on the table bottom are 'coplaner' to each other and parallel to the top surface of the table, and the trunions mating surfaces are 'coplaner' when attached to the tie bar, then the table and trunion mounting surfaces all will be 'coplaner' when secured with the screws. This does not create a change in the 'flatness of the table regardless of how much torque is used to tighten the mounting screws.

If however the table mounting bosses or the trunion mating surfaces are not 'coplaner', the table may be pulled out of flat when those surfaces are 'forced' to coincide by tightening the mounting screws. I think the table is the most likely part to deform.

It is difficult to determine this 'coplanerarity' due to the spacing and shape of the trunions etc.. However if the trunions with tiebar etc. are set upon the table mating surface(no screws) one could just look for any gaps. The presence of any gaps indicate where shimming is likely needed. However one must determine if more than one shim is needed to also maintain table top to pivot axis consistency between both pivots. Not doing so will likely create that heeling discussed over on the other thread. I do not know of an easy method to determine that consistency other than trial and error/correction.