Bandsaw - How Much Wobble is OK

[dusty]

This setup clearly indicates that there should be virtually NO movement of the legs when inserted (2" here) and locked.

Main Table Legs in Headrest

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Spindle Centered when Locked Locked

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[algale]

Ok, I have some measurable results.

The summary is this. First, none of the four cast "mounts" that the clamps slide into on my 520 are of identical thickness/depth. The variance between the pairs of mounts is greatest at the headrest end.

Second, to answer reible’s question, the clamping nuts are not being obstructed in any way by the casting mounts from entering the bores that the SPT tubes slide into.

Third, the bores for the SPT tubes are all fully and evenly machined on my machine.

Fourth, to varying degrees I have some wobble at both the headrest and base arm ends. I am not imagining it. It is there regardless of whether the SPT (I used the band saw) is clamped or unclamped.


Now for some photos and measurements.

I began by taking measurements of how far the clamping mounts protrude.

Headrest end, left side as you look at it straight on from the end. 0.434 inches.

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Headrest end, right side as you look at it straight in from the end. 0.530 inches.

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Base arm end, left side as you look at straight on from the end. 0.538 inches.

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Base arm end, right side as you look at it straight on from the end. 0.504 inches.

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Next, I inserted the band saw into head rest end, with zero clamping pressure (the clamp was actually removed for this test. I placed the Wixey on the band saw table and against the fence and zeroed it. Then I put my hand on top of the band saw case and pushed as far inward (toward the headstock) as possible. Even though the travel at the top of the band saw seemed to be at least an inch, the Wixey only changed its reading by 0.60 degrees.

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Staying on the head rest end, I adjusted the clamp to compensate for the mismatch of the depth the clamping nut must travel based on the measurements previously taken. After re-installing the clamp and applying normal hand tightening, I again zeroed the Wixey and again tried to push the band saw in. Less movement. 0.30 degrees per the Wixey.

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Moving to the base arm end, I repeated the same steps. Movement with no clamp. 0.50 degrees.

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After adjusting the clamp to take into consideration the difference in the clamp mount depths, the clamp was tightened with normal hand pressure. The deflection post clamping was 0.20.

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[dusty]

I think that we are all trying to pay the same game but on different ball fields.

If the bandsaw wobbles when mounted on the left end of the 510/520 with all locks and set screws secured there is a problem. I agree but I do not believe that we will find that wobble to be the result of scared casting bores.

Let us eliminate a couple of the obvious suspects.

Are the tubes (straight or eccentric) inserted up into the bandsaw until they meet the mechanical stops and are the set screws tight. If yes, is there any unwanted movement of the tubes? There should be NONE. The tubes should be rock solid (with respect to one another.

If this condition exists, the wobble is not caused by incompatibilities between the tubes and the bandsaw.

If you now remove these tubes from the bandsaw and insert the other ends of each into the Headrest (or Base Arm Assembly) and secure the lock, they too should be rock solid

Eccentric Hard Against Mechanical Stop

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Oter Eccentric Hard Against Mechanical Stop.

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Eccentrics Secred in the Bandsaw.

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[algale]

Dusty,

Do you get zero band saw wobble even without clamping pressure applied?

If there's preclamping wobble (but clamping eliminates it all), I'm curious if you could get some measurements like I took.

I don't think this is a question of scarred bores, either, since mine are well machined; although in other instances a bore that had a void in it might be a problem.

For the record, however, my eccentric tubes are properly inserted in the casting and the set screw is properly tightened.

Al

[dusty]

Dusty,

Do you get zero band saw wobble even without clamping pressure applied?

If there's preclamping wobble (but clamping eliminates it all), I'm curious if you could get some measurements like I took.

I don't think this is a question of scarred bores, either, since mine are well machined; although in other instances a bore that had a void in it might be a problem.

For the record, however, my eccentric tubes are properly inserted in the casting and the set screw is properly tightened. and I assume the eccentrics are immobile in the bores

Al

I don't get zero bandsaw wobble but it is very, very minimal and I don't believe it is wobbling on the tubes. I do have some movement prior to clamping but that is the result of the eccentric movement within the bores. Yes, I will try to get some similar measurements.

[dusty]

OKAY. It is time for humble appologizes. I apologize to all whose statements in this thread I thought were way out in left field. Far left (not a political statement).

My bandsaw is not near as stable as I thought it to be. The bandsaw table when level with no pressure applied moves (tilts) .35 degrees off level with pressure applied at the top of the bandsaw pushing toward the headstock. The lock reduces the movement somewhat but does not eliminate it. If you watch the eccentric tubes right where they meet with the headrest casting while you push and pull on the bandsaw you will see the tubes move.

The movement can be significantly reduced by extending the tube deeper into the casting but that cannot be done using the eccentrics. If the tube can be extended to 3" the movement is almost eliminated. The short eccentric leg is only 1 1/2" long. If the legs on the eccentric were equal in length to the long leg, stability would be achieved.

The burning question in my mind is why were they not done that way. Why is one side shorter? Oversight or deliberate for some reason.

It is possible (I would guess probable) that the movement could be eliminated completely by drilling and taping for set screws 90 degrees to the plane of the locking studs.

I would post pictures but I did a poor job of documenting the pictures as I took them. If necessary for clarification I can post some of what I have. Bottom line: I agree with your assessment of the problem, algale.

The various thicknesses of the castings are also as you said. They deviate from one another significantly but I think that is immaterial.

[algale]

Well, you are getting less movement (by almost half) than I am before clamping and probably even less after clamping.

Not sure what accounts for this variance.

[algale]

Also, Dusty, no apologies were necessary as far as I am concerned. This is how we work through issues on this Forum!

[dusty]

Thinking about this.

The movement that we are experiencing in this exercise may have something to do with why extension tables are not equally transportable from one end of the machine to the other without loosing alignment.

When I do extension table alignments, the tables are inserted maybe further into the castings than when I use them. Just a thought.

[jsburger]

I have been watching this thread with interest. Here is another data point.

I can't comment on the BS on the SS since mine has been on a power stand for almost since I bought it in about 1994. It has the eccentric tubes and as we know the power stand uses the Shopsmith Mounting Base -- 505655 to mount the SPT on the stand. The eccentric tubes are seated completely in the BS against the stops. There are a set of stop collars on the bottom ends of the tubes. They are tight against the eccentric step and tight against the mounting base. I assume this is what the instructions for the stand say. Too long ago to remember. Then the motor is adjusted down to tighten the belt. It has been working that way for 20 years or so. If I push back and forth on the top of the BS it moves a little bit but not much. There is no indication of anything loose, just the flexing of the entire assembly.

Now back to the OP's question. How much is too much? I don't know but the SS has been around longer than most of us. I was born 5 Jul 1947 so I guess I don't quite qualify but some of you do. There does not seem to be a problem with this in over 60 years. Are we collectively over thinking a problem that doesn't exist? Not a bad thing because it keeps the mind active and thinking. After all there has to be enough clearance between the mounting tubes and the head rest bores to get the SPT's on and off easily so there will be a little wobble.

To me the issue is how much this wobble contributes to the misalignment of the BS and head stock power coupler hubs during operation. The power coupler is flexible and designed for slight misalignment. Just as the coupler for the A34 jig saw on the 10ER or a Love Joy coupler. When you push the head stock up against the coupler and an SPT movement should be minimized.

JMO, and others will disagree but that is OK.