Weld sequence on V-Rails

[CCox]

I am a structural engineer and not familiar with the best way to manage weld sequencing to minimize distortion. I work in the wood products industry. The company I work for is replacing the v-rails and flat rails that band saws move along. I have attached the drawing of the existing system. The drawing on the left is a plan view showing the v-rails and flat rails. The v-rails are 18'-4" long, the flat rails are about 4' long.

Could someone provide guidance on the sequencing of the welding? For the sake of this, assume it is a 2" long 1/4" weld, spaced at 6" o.c.

Thanks.

 

[tbuelna]

Looking at the drawing provided, it appears the rail surfaces are machined after welding. In fact, the V-rails are precisely machined to mate with a specific gauge fixture.

If you intend to just weld new rails to the existing support structures, I don't think you'll be able to meet the accuracy requirements for the rail surfaces shown on the drawing without finish machining after welding. However, you'll still want to weld the new rails in place as accurately as practical, prior to finish machining. Align, shim and clamp the rails in place on the existing structure using a 3D laser alignment system. Then starting at the center of each rail section, stitch weld them to the support structure alternating side-to-side and end-to-end.

 

[MikeHalloran]

To do the required finish machining, you'll need a machine tool that's quite a bit bigger than the assembled bandsaw mill itself.
... and costs more.
... and rents for more in an hour than a brand new bandsaw mill would cost.
It's not a job for a Sawzall and a snag grinder.



Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

flat within 0.002" over an 18 foot long rail? wow

 

[CCox]

I will be doing the alignment using a Brunson Alignment Scope. With the scales I am using, it has an accuracy of .001" error over 17'.

As for the finish machining, what kind of options are available for a field application that I am dealing with? Basically, we have an annual shutdown and have 8 days to remove and install the new rails. Air pillows are being utilized to lift the band saws up from the rails to be able to accomplish the work.

The new rails will be a significant improvement over the existing rails that were installed 50 years ago. The current rails are so worn down at the cutting location that the saws actually roll slightly inward as the band saw wheels move along the rails. We align the saws in their cutting position to correct for this.

Thanks,

Cody

 

[Tmoose]

I'd be thinking about making precision Vees ahead of time, shimming for good alignment, then grouting them in place with filled epoxy or epoxy grout.

What are the wheels/tires like that run on these rails?

 

[MikeHalloran]

I think Tmoose is on the right track toward an acceptable solution.

I'd be inclined to have a set of rails made in a shop that can deal with long precise bars, and mechanically attached to the saw base, with no welding (and attendant distortion) involved. Maybe capscrews into blind tapped hole in the rail bottom or something like that. Instead of shims, I'd be inclined to try fine pitch setscrews through the rail, one adjacent each hold-down bolt, so you don't have to shave or sand shims to make fine adjustments. Locknuts and/or Loctite on the setscrews, of course, and epoxy grout after you've got the whole bed leveled and bolted down.

Please do let us know what you decide to do, and how it turns out.



Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

There are large gantry mills capable of finish machining the rail surfaces after welding with the precision required. But then there is the problem of transporting and re-installing the finish machined rail weldment with the same accuracy it had when fixtured on the milling machine.

 

[Tmoose]

These guys are fairly well known in the machine tool industry. Big claims for their products in direct contact with broad bearing surfaces (unlike what I picture based on your wheel description.)

http://www.moglice.com/handbook/handbook.pdf

Seem more than capable of securing properly prepared rails to a properly prepared bed, if the rails have a big enough foot print.

===========

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