The Infamous 4x6 Bandsaw square cut...

[markba633csi]

Ben: Have you checked the two main wheels for tracking in the same plane? Mistracking can cause the blade to try to leave the guides
Also what brand of blade are you using? Have you tried more than one brand? The HF ones are terrible, I've heard
-Mark

 

[BenG]

So update. (Thank you everyone for all the help so far I really appreciate it. It's been great having all you guys experience to help!)

Yes, using quality blades. The are a bi-metal from Blue Ribbon.

Mark, hmmm good point. I'll have to check that again. I did when originally setting it up and the bottom wheel had to be moved out. There are two screws on the top wheel that seem to adjust the tracking, thinking now, if I just cranked them both in, wouldn't this just move the top wheel in?

Oh and getting serious now. No going back..

 

[C-Bag]

Just out of curiosity have you found the culprit? IMHO leaving the guide bearings loose enough to turn by hand means they might be tight or not and you don’t know how much they are not keeping the blade straight. There is so much twisting they are doing how you know if they are actually doing their job?

I’ve never been one to change to many things at one time because it might either mask or compound problems.

you mentioned if you got the guides tight the blade mis tracked? Are the guides square to the blade track?

Did the blade go out of square as you moved the head through its travel? And that’s why the major surgery on the pivot point?

 

[BenG]

C-Bag it appears as if the main root culprit is the pivot being outbid square to the table. Even only at 5.5" up in the swing of the blade it was out of square about .090". Now this seems to make sense as the best I was able to get it to cut was a C shaped curve with both start and end of the cut being pretty close to square and then the middle being curved. Which happened when I had the guides set right and pointed slightly in towards the saw so started off cutting in then as it cut at an angle to the pivot the twist epild eventually overcome the dropping pressure and it would cut curving back out. Does this sound right?

I did a bunch of messing around the guides and bearings, tight, loose, etc. You are right, it seemed to work best tight to the sides of the blade so that I could just not turn them and the blade didn't have any twisting slop.

How much play is everyone seeing in their guide bearings? I did notice a little play and wonder if it's time to replace the bearing? Maybe this is contributing to it not tracking as Mark mentioned?

 

[markba633csi]

By play in the guide bearings you mean wear in the ball bearings themselves? Probably not significant if they are less than a couple years old
This application does put a fair amount of stress on them however, and the factory parts are probably not super great quality. Your call.
I think you are kind of correct about the curving cut behavior more or less. The pivot of course adding much of the error. Are you going to reweld the ears back or make a substitute pivot piece? I would probably opt for the latter to have the ability to shim and adjust

You can add/subtract washers to the post that the non-driven wheel mounts to in order to align the wheels, in addition to the adjuster setscrews on the mounting block. The driven wheel can also be shimmed, if need be. (I needed to on mine) Extra time spent here really pays off, I've found.
The blade should make contact with both wheel rims and the small back bearing on each guide simultaneously in a well-aligned saw
If you don't have a straight edge a good straight board edge will do. I think I used a piece of angle iron from a bed frame

 

[BenG]

Mark, yes in the bearings themselves. There is some slight play in them. I'll see about getting some replacements (I believe these ones are quite old!).

So, I ended up cutting off the ear away from the blade, welding tabs on to it, milling a flat spot where it was previously located, drilled, welded a tab on the saw base, drilled and tapped two holes and mounted the now movable pivot back on. Shimmed the pivot so the blade pivots square to the table, and success! Straight cuts!

I did end up going back through and checking the wheels, and making sure the tracking was good (just touching the wheel rims etc.), and also adjusting the guides square and in/out so they contact the back of the blade properly.

Man, it cuts pretty well right now (I didn't jinx it did I?)

Thanks guys for all the help, I was getting pretty frustrated with this. Great suggestions, and making me go back and re-do and check things again which really made a difference!

Happy to post up some photo's if anyone is interested in seeing it.

 

[7milesup]

Happy to post up some photo's if anyone is interested in seeing it.

Pffffttt... ummmm yeah! Pictures or it didn't happen!

 

[BenG]

Here's a couple of photo's of in process and finished. Probably would be good to replace the lug with a maintainable bearing in the future?

 

[C-Bag]

You know since the description you mentioned of the cut being a curve I’ve been coming back to that over and over. I just can’t wrap my head around just how the pivot point could cause being at one relative angle at the top of the cut and another at the bottom. I can totally see how they could bore the body pivot ears not square and level. But it gets beyond my ability to visualize how maybe the pivot point on the saw head being bored wrong too and how that relationship between the two would end up making a curved cut. It’s kinda driving me crazy like I’m running out of memory or hdd space

lots of work, nice fix, good work.

 

[John O]

You know since the description you mentioned of the cut being a curve I’ve been coming back to that over and over. I just can’t wrap my head around just how the pivot point could cause being at one relative angle at the top of the cut and another at the bottom. I can totally see how they could bore the body pivot ears not square and level. But it gets beyond my ability to visualize how maybe the pivot point on the saw head being bored wrong too and how that relationship between the two would end up making a curved cut. It’s kinda driving me crazy like I’m running out of memory or hdd space

lots of work, nice fix, good work.

I will try, the cut starts on an angle pulling the blade away from the saw, tension on blade increases till it pulls the blade back towards the saw.