Homemade Dimensional Sawmill

[Jeremy Maso]

Hi! I'm working with Open Source Ecology in developing a homemade "open source" dimensional sawmill. I've got most of the design drawn up but am stuck on some parts that I need more information on. You can read about the basics on our blog here and see the development page here.

So far we've decided on a design similar to the Mobile Dimension Sawmill, with a space frame (for stability) on two "I" beams for x and y axis movements, a chassis surrounding the space frame with bearings to grip it on all sides, a vertical plate or beams on the chassis with another plate attached with bearings and adjusted vertically with a pulley for the z axis, the saws are mounted on the vertically moving plate and powered with hydraulic motors. We are using the hydraulic pump on the open source LifeTrac tractor to power the motors.

My questions are:
1. Will the current design of the rollers/bearings work? Will they have trouble going over sawdust that gets on the track? Are they strong enough to hold the saws and everything(250-300 pounds)? Is it going to be too hard to build the cage to get them to fit on the space frame tightly so it doesn't wobble around and make bad cuts? Here's a picture of the current roller/bearing design. The bearings are these ones. They are flat rollers on a bolt with spacers in a kind of U-channel bolted to the cage. They have 3 bearings on each set in the picture, but we're thinking of using just 2 on each set. They roll on the flat sides of square tubes that are the edges of a space frame. All sets are the same on top, bottom, and sides.

2. How are the rollers/bearings on other sawmills with moving saws designed? I would guess that many CNC machines would also have rollers that would be similar. Are there any pictures or online patents or design details on how other rollers work? I've heard that there are some that have a V shapped bearing in a groove to work like a track, is that what we're going to have to do? Are there any pictures of anything that uses that method? I have also seen some bearings with springs on the shafts that pull them tight against the surface they roll on.

Thanks for any help!

 

[Leejohn]

Leave the flat on the bottom and us the V on top with wipers to clean off the saw dust. I would use larger bearings and a good size V roller even if you have to make them.

 

[aczlan]

Looks like an interesting project, for more ideas/help on the tractor and attachments, you might try machinebuilders.net, they are dedicated to building equipment.

Aaron Z

 

[Jeremy Maso]

Leave the flat on the bottom and us the V on top with wipers to clean off the saw dust. I would use larger bearings and a good size V roller even if you have to make them.

Thanks for the feedback! I'll work on a V roller design tomorrow. We were looking into possibly using inline skate wheels and I'll look into using bar channels for the track. I think I'll also go with springs on one of the sides and the bottom to maintain a good grip on the frame.

Looks like an interesting project, for more ideas/help on the tractor and attachments, you might try machinebuilders.net, they are dedicated to building equipment.

Aaron Z

Thanks, I'll check it out!

 

[towmotor]

Just a quick observation here:
I looked at some of your renderings, and from what I saw, it appears that you're not using any welded connections (am I wrong?).
The bolted connections will undoubtedly loosen over time and cause the sawmill to become inaccurate and possibly dangerous. You should seriously consider welded connections on the carriage assembly at the very least.

One other thing, and perhaps you or the others who've posted here have considered and rejected:
If it was me designing this rig, I would consider having the carriage rollers ride on the toe of angles instead of on the flats of square tube.
That way, you could use a sheave (thin grooved wheel) (garage door pulleys?) instead of the wide wheels.
If you did this, then you wouldn't need to be as concerned about sawdust accumulating on the horizontal surfaces, since the horizontal surfaces would be 2 or 3 inches(depending on what size angle you use) from the carriage wheels.

By the way, square tube is beautiful stuff, but it's quite expensive and fit-ups for welding are more difficult. Angle should do the job, particlularly with that trussed track you're building.

In case you haven't done so already, you should check out McMaster-Carr- a huge source of parts and materials for just such a project. (no, I'm not on their payroll)

 

[Leejohn]

You can buy steel V casters and just use the wheel. I think you need a little bigger wheel.

 

[Jeremy Maso]

Just a quick observation here:
I looked at some of your renderings, and from what I saw, it appears that you're not using any welded connections (am I wrong?).
The bolted connections will undoubtedly loosen over time and cause the sawmill to become inaccurate and possibly dangerous. You should seriously consider welded connections on the carriage assembly at the very least.

One other thing, and perhaps you or the others who've posted here have considered and rejected:
If it was me designing this rig, I would consider having the carriage rollers ride on the toe of angles instead of on the flats of square tube.
That way, you could use a sheave (thin grooved wheel) (garage door pulleys?) instead of the wide wheels.
If you did this, then you wouldn't need to be as concerned about sawdust accumulating on the horizontal surfaces, since the horizontal surfaces would be 2 or 3 inches(depending on what size angle you use) from the carriage wheels.

By the way, square tube is beautiful stuff, but it's quite expensive and fit-ups for welding are more difficult. Angle should do the job, particlularly with that trussed track you're building.

In case you haven't done so already, you should check out McMaster-Carr- a huge source of parts and materials for just such a project. (no, I'm not on their payroll)

We're mostly using bolts so things can easily be adjusted and disassembled for repair or changes in design for further prototypes. If things look like they're getting too loose then we can use welds. I guess I also hadn't considered welding much since I'm not too familiar with it yet.

It looks like V groove wheels are the way to go. I think I've found some good deals on some V groove wheels at acecasters.com for $7.56 and Grainger for $7.57.

Square tubing was recommended because of the better strength of a square tube compared to the same amount of metal in an angle. I'm going to get a computer aided engineering program and do some tests to see if it actually works out like that. It's going to be more work to make two sets of holes for each bolt on the square tube though, so I'd prefer the angle. Another factor of the square tube is that it can be reused for another project at some point if we end up scrapping this prototype.

I've added McMaster-Carr for reference on the basic parts sourcing page, thanks!

You can buy steel V casters and just use the wheel. I think you need a little bigger wheel.

4 or 5 inches should be good, right? How do these ones look? 1 "CAST IRON WHEELS INCLUDE: WHEEL, ROLLER BEARINGS, SPANNER, GREASE SEALS, AND LUBE AXLE. THE WHEELS ALSO HAVE A GREASE FITTING. 4x1.5 inches" - 2 "5x2 inches"

 

[Skyco]

We're mostly using bolts so things can easily be adjusted and disassembled for repair or changes in design for further prototypes. If things look like they're getting too loose then we can use welds. I guess I also hadn't considered welding much since I'm not too familiar with it yet.

You can always use locking fasteners or a locking compound to secure if welding is a problem.

 

[towmotor]

Square tubing was recommended because of the better strength of a square tube compared to the same amount of metal in an angle.

Jeremy,
I don't want to labor the point past it's due, but you're right-square tube is a better choice , as a stand alone piece of structure, than the equivalent weight in angle.
However, there are a few things for you to consider here:
1) From the illustration you linked, the tube is not being used as a stand-alone structure. It is being used in a trussed structure, where the loads are primarily in one (the vertical) axis, meaning that you could use angle.
Consider, if you will, a radio tower. Very strong, trussed structure. Not much, if any, tube to be found there. Lots of angle

When you prepare the pieces for welding (and you will weld-it's more economical and faster to build, not to mention stronger, more about welding later) angle is the surefire way to go for a novice.

2) All steel sections-tube, angle, I-beam etc- have mill tolerances that allow a considerable amount of dimensional deviation, twisting and bending. You'll undoubtedly encounter this when you're assembling a track that's twenty(?) some feet in length.
Tube, precisely because of it's multiaxial strength, will be much harder to deal with, in terms of rectifying these deviations, than angle.

3) As I mention in my first post, a wheel riding on the toe of an angle, will be two or three inches from the sawdust accumulating on the perpendicular flange, making the clumps of sawdust almost of no effect in terms of accurate, smooth carriage travel.
Compare this with the problem that you acknowledge it will present with tube...

4) About welding your carriage: I understand your concern with adjustability in your carriage. Adjustability is an absolute must, but it should be at controllable points rather than spread over the entire carriage assembly, which is exactly what you'll have with all of those sloppy bolted connections, even if the bolts remain tight.
You need to know that once you align the carriage with the track(using controlled adjustment points/procedures), the entire carriage will remain in alignment with itself,even if you've had slight dimensional screw-ups in welding the carriage together. Once you've established this carriage/track alignment, you can align the saw blade with reasonable confidence that you're building on a solid foundation.

5) About "welding" itself:
Don't be intimidated by the thought of welding. Making acceptable welds (for your purposes) is something that you should be able to master in just a few hours.
It's a valuable skill to build upon, and once you've become more aquainted with it, you'll be able to expand the possibilities of what you can build/design yourself.
Your not building a suspension bridge, a pipeline, or even a radio tower. It's a sawmill, with very simple joint/welding requirements that will be so much stronger and dimensionally stable than bolting, with less effort in the long run.
It could...no, it will ultimately make the difference in whether or not this sawmill will work or be a source of frustration.

I'm trying to help you out.
I've been building and designing steel structures with mechanical interfaces for almost thirty years, so I'm not just guessing about this.

Good luck with your sawmill, and when that works (it will), good luck with the future.

 

[F.L. Jennings]

Your project sounds interesting, especially being a former sawmill owner and a senior designer at an engineering company that specializes in the forest products industry. We design sawmills, chipmills, mdf/hdf plants, plywood mills & so forth.

Here are some notes;

1. Mount wipers in front and behind each wheel to push away sawdust. You can even make each one a double wiper. A piece of UHMW plastic cut o fit within 1/16 to 1/32" of the track for the inner, and out in front of that say an inch or so a brush. This way you can really take care or getting the sawdust off the track. Low pressure air can be used in lieu of this or as an added feature. The circle saw mill I owned had wipers either side of the carriage wheels. The wipers should be made such that they push sawdust and debris so that it can drop totally out of the way and not build up in any way to fall back on the track(s).

2. The rollers do not have to be made but can be purchased commercially. Both the flat type and the V rollers are readily available. They can be either with a threaded stud or with a bore hole for mounting on your own shaft or stud. McGill is one bearing manufacturer that makes these. Just google "cam rollers" and a host of providers will pop up.

3. One way, a traditional method, to mount wheels, is based on the following theory. Since metal carriages contract and expand with temperature changes (delta t) one set of wheels is the "V" type and the other set(s) is the flat type. This anchors (more or less) a part of the carriage assembly, while the flat rollers allow expansion in that direction. Studded type shown in photos.

4. For guiding any components or assemblies, the thomson ball bushings and hardened shafts are very good. The shafts are case hardened and come in a variety of sizes, as do the different configurations (pillow block type, cartridge type, flange mounted type) of linear ball bushing bearings. http://www.danahermotion.com/website/com/eng/products/linear_guides/linear_bearings.php Complete downloadable catalogs are readily available.

Frank Jennings
Senior Designer
Mid-South Engineering Company
mseco.com