phone  (937) 890-5197

Shopsmith Forums

%nbsp;

43 posts 1 2 3 4 5

Bandsaw - How Much Wobble is OK

#264710 by DLB » Mon Nov 18, 2019 2:10 pm

I recently picked up a new-to-me 2004 Model 520 and 2001 Bandsaw. Since the early 80's I've used a late 50's Greenie with Magna Bandsaw (some upgrades) and Magna Jointer. For this thread I'm primarily contrasting the 2001 Bandsaw with the Magna.

Initially, the 2001 bandsaw was extremely wobbly but I aligned it and tried to use it. I broke two couplers, first one of the old yellowish-white translucent ones that was probably original equipment on my Greenie and then a newer opaque white one. I initially ignored the first coupler failure, 60+ years seemed okay. But after the second I read a thread here on coupler failures and decided that wobble was like mis-alignment, and now think I overheated the coupler. I worked out that my Accessory Mounting Locks needed asymmetric adjustment because of some manufacturing variation and that has greatly diminished, but not eliminated the wobble.

Before I figured out the lock/clamp problem I mounted the Magna, which had significantly less wobble even without tightening the lock. And I had never had to adjust the locks more than snug with the Magna. With the new bandsaw I find that the tighter I make the locks the more I decrease wobble, even going beyond hand tight.

The Magna has straight mounting tubes where the newer model has the eccentrics. (Small 1/4 inch eccentrics, not offset tubes.) In addition, there are several dimensional differences and features that seem to make the new tubes prone to wobble. Since most readers don't have a straight tube mount to compare, the tubes are similar to those on an extension table. The straight tubes have no horizontal adjustment, vertical adjustment is done with stop collars. I aligned both on the same SS 520 and then removed a tube from each to make these measurements and observations. Objective measurements are eccentric first, followed by straight tube, in inches:
Overall length: 6-7/16 Vs 7-1/2
Length above mount surface: 4-1/4 Vs 4-9/16
Flats above mount surface (ignoring bevels): 4-1/8 Vs 4-1/2
Flats below mount furface: 2.077 Vs 2.841
Corrected: Tube diameter: 1.231 Vs 1.239 (Avg of 6 measurements, variation was +/- .001)
Observations:
1)The end bevels on the aluminum eccentrics are much more pronounced than on the straight steel tubes. This is important to this thread because only the flat, non-beveled, portion provides support.
2) The straight tube gives much firmer engagement in both bandsaws with the set screw loose. It fits snugly into both collars and goes in all the way to the mechanical stop. The bandsaw setscrew does almost nothing. In contrast, the eccentric fits loosely. It will go in to the mechanical stop but vertical adjustment takes it well off the stop and leaves it only partially engaged in the upper collar. The setscrew is working hard, forcing engagement between the tube and lower collar. Some wobble may come from the lack of engagement between the tube and the upper collar, contributed to by both the smaller diameter and the shorter length of the tube.
3) Similarly, the straight tube gives much better engagement below the mounting surface in the SS headrest. The headrest mounting holes are about 2-3/4 deep, so the eccentrics don't use the full length. With the lock (SPTclamp) loose, the eccentric is a pretty sloppy fit in the mount compared to the straight tube. The smaller diameter and shorter length both contribute. Even the small shoulder of the eccentric compared to the stop collar contributes. Similar to the set screw in the lower collar of the bandsaw, this requires the lock/SPTclamp to do a lot more work to reduce wobble on the eccentric mount.
4) In addition to expecting the lock to do a lot more work, I observe that it is not in the best axis for doing that work. Bandsaw wobble is left to right, toward and away from the headstock. Clamping force is front to back. This seems consistent with my earlier observation wobble diminishes with greater clamping force, including more than I think is intended (beyond hand tight.)
5) Nothing I've seen leads me to think that the eccentricity itself has much to do with wobble. I think the biggest contributor to wobble is the smaller diameter of the eccentric tubes.

I still have a few things to do when I put the bandsaws back together, and re-align them. But based on my observations and measurements, I think that the wobble I am experiencing now is largely inherent to the design of the eccentric tubes, or at least the ones that I have. I became very sensitive to the wobble after breaking couplers, and initially expected to get the wobble down to a level that the design perhaps no longer supports (Magna-like). Also I need to change my expectation that snug engagement of the lock/clamp should be sufficient. Much firmer engagement is needed for the eccentrics.

I've seen several threads that included bandsaw wobble, but I doubt if I've seen them all. Am I missing anything that would explain this better, or perhaps some trick(s) to improve?
Last edited by DLB on Tue Nov 26, 2019 1:43 pm, edited 1 time in total.

Post a reply  Reply with quote 

Re: Bandsaw - How Much Wobble is OK

#264714 by P89DC » Mon Nov 18, 2019 4:07 pm

I have one bandsaw with eccentrics and one with straight tubes. I haven't been able to line up the straight tubed bandsaw as well as the eccentric one (which is perfectly lined up). As for wobble, I don't notice any difference between the two. On my next order I'll add some eccentric tubes for my older bandsaw because they work so much better than the straight ones.

As for have a coupler blow up, that seems as if something is really wrong. I have 40 year old couplers that are still fine.

---

1986 510, jointer, bandsaw, belt sander, scroll saw, jigsaw and lots of accessories. Shopsmith woodworking bench too!

Post a reply  Reply with quote 

Re: Bandsaw - How Much Wobble is OK

#264737 by dusty » Tue Nov 19, 2019 6:48 am

Wobble - "caused by the eccentric tubes". I don't think so! Unless the eccentrics are not secured. Without the SPT attached but the eccentrics inserted - do the eccentrics wobble?

---

"Making Sawdust Safely"
Dusty
Sent from my Dell XPS using Firefox.

Post a reply  Reply with quote 

Re: Bandsaw - How Much Wobble is OK

#264738 by algale » Tue Nov 19, 2019 7:05 am

All my SPTs, including one of my band saws, are on the newer non-straight tubes and they all exhibit some obvious amount of play or wobble toward/away from the headstock after clamping but before the SPT is connected to the headstock via the power coupler.

Once the power coupler is attached to the SPT and the headstock is pushed snugly up against the coupler, I find the play is largely eliminated and certainly nothing that has had any adverse effect on any project I've done on my Shopsmith using a SPT.

On the other hand, I have a second band saw mounted on the special "eccentric tubes" that Shopsmith introduced to allow the band saws with the "new" aluminum table to remain attached while the Shopsmith is raised to vertical drill press position. That offset eccentric is two separate steel tubes connected by a flat piece of steel. https://www.shopsmith.com/ownersite/cat ... gtubes.htm They must have used "spring" steel, because that eccentric has a great deal of bounce to it and is very annoying in operation.

---

Gale's Law: The bigger the woodworking project, the less the mistakes show in any photo taken far enough away to show the entire project!

Post a reply  Reply with quote 

Re: Bandsaw - How Much Wobble is OK

#264754 by DLB » Tue Nov 19, 2019 12:20 pm

To answer Dusty's question: I started to say No, I had tried that yesterday with an eccentric in the back and a straight tube in the front and I didn't detect any wobble. This morning I put in two eccentrics and the behavior surprised me. When I tighten the clamp snugly, the back one is tight and the front one wobbles. I can tighten it quite a bit more and the front one still wobbles. I have to tighten it extremely tight to eliminate the wobble. I swapped the eccentrics and the front one still wobbled much more, the behavior stayed with the hole rather than following the mounting tube. I had definite, relatively wide gaps on both ends of the clamp handle throughout. I tried the straight tubes, no wobble in either one from snug onward. I don't even have a viable theory for this, but as I mentioned in the "SPTclamp" thread, where I included pics, I have some asymmetry in my headrest casting and I have to put some asymmetry in my clamp adjustment to offset it or the clamp will bottom out while only clamping one tube. (That was the original problem when I had A LOT of wobble and the couplers failed.) I don't see the relationship, but I'm not inclined to think it is a coincidence. More investigation is needed.

I installed the straight tubes in the newer bandsaw and it is noticeably more secure, at the cost of not being adjustable. This is exactly the result I expected.

Post a reply  Reply with quote 

Re: Bandsaw - How Much Wobble is OK

#264755 by nuhobby » Tue Nov 19, 2019 12:31 pm

My own experience is exactly as described by algale above.

Moving on from static wobble to dynamic wobble concerns, I have a 2007 bandsaw and it had always moved a fair deal (dynamic wobbling) when driven. A couple years later I actually bought a bandsaw-rebuild kit from Shopsmith to restore a very old BS for my brother-in-law. I then had 4 new-ish aluminum bandsaw wheels which were all drill-balanced but all rather asymmetric-looking in terms of casting accuracy. I was able to mix & match wheels between the machines so that my 2007 BS got less dynamic wobble than before, and the very old BS came out also with minimal dynamic wobble.

- Chris

Post a reply  Reply with quote 

Re: Bandsaw - How Much Wobble is OK

#264797 by JPG » Wed Nov 20, 2019 8:11 pm

I have resisted posting here, but now here goes.

The base castings do vary. I am surprised the the difference between the two clamp mounts is so severe. That does require off setting the clamp studs.

Now how is the clamp supposed to function? It is quite simple. The studs advance outward from the 'knurled' sleeve as tightening takes place. The studs then exert force against the mounting post(s) and must do so without the sleeve contacting the base casting. IF only one stud is pushing the mounting post against the far wall of the casting, only half the clamping action is being effective. Proper clamping results in both the tubes being forced out against the outer walls of the casting. That should eliminate front to rear wobble(assuming all else is also secure (tube in BS casting etc.)). Note BOTH tubes do not have any 'play' in the base casting bores.

However the issue being discussed is side to side wobble. Regardless of the straight/eccentric mounting tube sizes the tubes need to be inserted all the way into the mounting holes in the BS casting. I have not been able to do so with the newer eccentric mounting tubes. I think the eccentric tubes are too short to do so. That requires the tubes be retracted slightly out of the BS casting which reduces their effective stability.

BTW the way to reduce the spring board effect with the off set tubes is to beef up the connecting plates.

Yes longer tubes inserted into the base casting will help reduce wobble just as also doing so at the bs casting mounting. I do not think the bs eccentric tubes are long enough at either end.

---

╔═══╗
╟JPG ╢
╚═══╝

Goldie(Bought New SN 377425)/4" jointer/6" beltsander/12" planer/stripsander/bandsaw/powerstation /Scroll saw/Jig saw /Craftsman 10" ras/Craftsman 6" thicknessplaner/ Dayton10"tablesaw(restoredfromneighborstrashpile)/ Mark VII restoration in 'progress'/ 10E(SN E3779) restoration in progress, a 510 on the back burner and a growing pile of items to be eventually returned to useful life. - aka Red Grange

Post a reply  Reply with quote 

Re: Bandsaw - How Much Wobble is OK

#264830 by DLB » Thu Nov 21, 2019 2:10 pm

I put the eccentrics by themselves, then with the Bandsaw, in my Greenie and it was much more stable both ways, in comparison to the 520.

Back on the 520 I tried several things with the SPTclamps. I tried reducing the offset as much as I could get away with, reversed the clamp to 'outside down to tighten,' tried the other clamp, nothing seemed to help. With some difficulty I even tried the 'vintage' clamp that worked on the Greenie and that did not help either. I was working on the theory that something about that offset I needed for the Headstock casting feature was relevant. Testing the theory seemed to disprove it.

Next I tried some eccentrics from a belt sander, but with no SPT. They are the same or very similar to those for the bandsaw. They had some light oxidation, so they allowed me to see the contact points after I clamped them down in the 520 headstock. They behaved the same as the ones from the Bandsaw, with the front one requiring much more clamp pressure to stop it from rocking compared to the back one. The only pressure points on the front one were from the SPTclamp and essentially directly across from it, evidently indicating a slight high spot in the Headrest mounting hole. In essence, with only two effective clamping points 180 degrees apart it is acting as a hinge. In contrast, the rear eccentric showed three clear contact points on the side opposite the clamp, one essentially directly across, but also one above and one below that. Obviously that is much more stable.

At this point I am satisfied that I understand the behavior. I don't see a direct relationship with the Headrest mount casting asymmetry other than proximity. I do have a theory that ties them together, but I can't prove it: The PO was unaware that he was only getting good locking performance in the back mount due to the casting asymmetry, and had some front/back rocking with some SPTs, resulting in uneven wear in the front edge of the front mounting hole, and leaving a high spot near its vertical center. IIRC I originally noticed the locking problem as a front/rear rock with my Magna Jointer, which has solid steel eccentric mounts with dimensional differences that make them a relatively snug fits compared to the aluminum versions. For now I'm sufficiently confident in this theory that if my solution includes procuring a used headstock, it won't be one with the visible difference between the clamp mounts unless I can test it first.

-David

Post a reply  Reply with quote 

Re: Bandsaw - How Much Wobble is OK

#264833 by reible » Thu Nov 21, 2019 3:19 pm

Has anyone with this problem tested to see that the bolt heads are free to move into the holes? Pull the tubes and keep extending so the bolt heads are protruding well into the holes with no obstruction might be a worth while test.

With some of the pictures posted with the uneven left/right bosses it could be that there are other defects in the parts.

Speaking of which this might be a defect worth pursuing with Shopsmith. You know are life long woodworking partner who may have supplied defective parts on your machine and might be willing to fix the issue.

Ed

---

{Knight of the Shopsmith} [Hero's don't wear capes, they wear dog tags]

Post a reply  Reply with quote 

Re: Bandsaw - How Much Wobble is OK

#264849 by JPG » Fri Nov 22, 2019 1:10 am

The differing clamp 'sockets' are in and by themselves suspect as to quality issues.

If the front tube was not being securely clamped, wear is quite possibly causing insufficient clamping.

Only the base casting need be replaced if all that is the case.

I am curious if this problem also exists at the right end.

---

╔═══╗
╟JPG ╢
╚═══╝

Goldie(Bought New SN 377425)/4" jointer/6" beltsander/12" planer/stripsander/bandsaw/powerstation /Scroll saw/Jig saw /Craftsman 10" ras/Craftsman 6" thicknessplaner/ Dayton10"tablesaw(restoredfromneighborstrashpile)/ Mark VII restoration in 'progress'/ 10E(SN E3779) restoration in progress, a 510 on the back burner and a growing pile of items to be eventually returned to useful life. - aka Red Grange

Post a reply  Reply with quote 

Who is online

Users browsing this forum: No registered users and 38 guests

Board indexDelete all board cookies

Welcome to Shopsmith. Please fill in this form and we'll send you more information and special offers for the Shopsmith MARK 7 and other woodworking topics.

Subscribe to our mailing list

* indicates required