heavy duty linear slide

[brettawilson]

I am looking for heavy duty linear slide setup with the capacity to hold 750-1000 lbs. Tricky part is I would like the slide to have a 20' length. I would like to use on a sawmill. I have looked around and closest thing i have found is

http://www.cnczone.com/forums/attach...4&d=1150319068

I am looking to purchase, does anyone know of a manufacturer for a heavy duty linear slide in 20' length? Or, alternatively i can build one but I only have welder, drill press and other basic metal tools. Any ideas on a diy linear slide with that kind of weight capacity?

[BrendaEM]

I wonder if you could machine an section of railroad rail to suit your needs.

Um, please don't remove rail from where it might still be used.

[vacpress]

heh.

THK type linear rails can have their ends machined to overlap, providing long rails. This type of system will cost between $100 and $500/foot, i would estimate.

What sort of accuracy do you need?

750 to 1500lbs isnt that much weight really. But the forces involved if that is the weight of the lumber being moved may be much higher...

Your question is far to vauge. You need to specify budget, accuracy requirements, types of forces the unit will expect, environmental issues such as how much dust or liquids the device will come in contact with

cheers.

[InspirationTool]

You may want to look at doing and angle iron set up like the travels for a shopbot router.

-Jeff

[brettawilson]

Thank you for the great suggestions. I appreciate the thoughts and contributions from all of you. That thk choice is out of scope for my budget. As I am a diy'er on a limited budget i think I will go with the 4" casters on 3/16 angle iron. The casters are rated for 800 lbs each and i will use 4. Looking at putting on an adjustable bottom set so that there is no skipping or jumping of the carriage, something like a dual rail setup. Not sure if it is necessary to be honest, seems like overkill.
In terms of accuracy I am trying to get as accurate as possible, but within a reasonable budget. The same old issue every diy'er faces. Accuracy in the mill means a consistent width in the boards which will be easier to work with in terms of woodworking (less machining, planing, sanding). The key is that the log stays on a heavy steel bed and that a carriage moves over top of the log. The carriage is carrying 250 lbs of band wheels, a 700lb 30 hp diesel engine and various bearings, shafts, a clutch, some blade lubricator and the carriage assembly. I estimate it all at 2000 lbs. There are no lateral forces on the rail system, they are all horizontal and vertical. These vert and horizontal forces will change with blade cutting capacity. Meaning the duller the blade the more horizontal and vertical forces, also wood density such as knots will influence these forces.
Thanks again for everyones input.

[Stepper Monkey]

The loads imparted to the rail from cutting lumber like that with that much weight on the carriage will cause HUGE twisting and flexing of a rig built out of angle no matter how thick or how many of them. I don't care how much weight it can support, it is not going to have any rigidity to handle the transient forces. That thing would occillate and buck around like mad with that system.

I would actually suggest seriously looking into the railroad rail possibility, or even structural I-beam. It's cheap enough, and you really would need it.

You still would have to have several intermediate braces to shorten free span, and have carriers with wheels not only running atop to hang the load, but also running underneath the carriage, as well as a couple of wheels opposing one another running along the horizontal member to hopefully quash lateral movement.
Why do you need to suspend and move the whole cutting assembly and motor anyway? Wouldn't they be better fixed relative to the system?

Amount of weight the rails can carry isn't really relevant here once the thing starts trying to cut into something. Torsional and flexural rigidity are gonna be the sticking points here, most likely involving long sharp pointy machine fragments sticking out of the operator if they aren't calculated correctly!

[vladdy]

when I built a bandsaw mill a few years ago, I used 2x4x0.250 for the main frame [or bed], with cross supports every 18"..it worked ok for up to 24" diameter poplar / spruce..
I also used the 5" diameter V wheels and welded 2x2x0.250 angle iron on top of the main bed upside down ..these were 'fair' for self cleaning, but a piece of canvas made an excellent wiper..
The uprights were 3x5, and the main cross was 3x8 as it supported the motor etc..
I used roller chain and sprockets for the lift, #50 as I recall, but still needed to counterbalance with about 500 lbs of lead pots as it would have a tendancy to 'creep' down occasionally even with the friction lock tightened, plus it was a lot easier to return up at the end of a cut so the blade wasn't dragging across the top of the last cut..
I ran a briggs vangaurd 20hp twin, and power was good on pretty well everything except old maple..
All was pretty well mechanical, no hydraulic assist or drive, I used a reduction belt off the blade drive to a weighted rubber tire for feed drive and return, it had just enough normal slippage to allow it to reduce feed in tougher pieces, and normally moved at just a medium walking pace..maybe 3 1/2 mph or so..
I used a small 3 gal drip feed for blade lube, and normally would get 5 to 6 hrs of cutting before changing [I resharpened at home later on]..

[justCNCit]

stupid question, but that setup that was linked in the first post, would any of you guys ever consider building a CNC mill using that thing?

[Zumba]

Originally Posted by justCNCit stupid question, but that setup that was linked in the first post, would any of you guys ever consider building a CNC mill using that thing?

I wouldn't. As cool as it may look, the labor, cost of materials, and overall design of it makes it an impractical alternative to commercially available bearings and rails.