Most welding projects that require a high degree of trueness are welded in preset jigs. Other folks, if lucky enough to have a level cement floor and a chalk box can also do a fairly good job. I would like to know some tips and advice for welding true and straight truss type beams. For an example lets just say a fellow wanted to build his own mill similar to a Mighty mite or Mobile Dimension, but needed to weld the main beam(s) using substandard methods. ::) Country techniques are most welcome.
Would buying some old roof trusses be worth while?
If you have some experience in welding fabrications you can limit the amount of heat distortion by designing your fabrication to be welded in neutral axis as much as possible. The other item needed is a straightening press, or a torch to staighten the crooked parts.
Instead of welding you can also use bolted joints were possible to reduce the amount of bends caused by welding.
Simply using a string &/or a laser will get you a striaght line to reference.
Making sure your joints are fitted right and clamp nice and tight are a big important.
I agree what Gilman said also.
When building my mill I used a 6 ft level, string, and eye sight.
EZ
How about a country application of a modern technique? You can build your own laser level real easy from junk laying around the shop in your way. ::) Just take an old hub with good bearings in it and build a base for it where it will be level. IE, the axle is perpindicular to the ground. Fasten one of them cheapo laser levels to it and rotate it by hand. Any place that little laser dot appears is in the same plane as any other place the dot touches. It may not be perfectly level, but it'll be in the same plane, and that's what matters.
Quote from: Gilman on September 30, 2005, 11:39:48 PM
Instead of welding you can also use bolted joints were possible to reduce the amount of bends caused by welding.
Gilman, that is probably the best thing to do and then weld it as well. I've welded things in the past and made scribe marks using a slide square and center punched the station points to drill and bolt. Everything was true, it just takes a while...........Another thing I would like to ask you MD and MM owners, as long as that beam is, do you think maybe that it has a little bit of crown? Just enough to counter the weight of the beam and motor?
I'd definitely crown it.
A four foot level and carpenter square ... get yourself level on sawhorses ... Use the square and tack weld your peices , you can wack them true after they are tacked if not square . Check your square often and dont weld on same side to much .. try to get two faces welded up as you are welding ... to prevent distortion .
You can buy or borrow a welding square ... just a square with magnets ... they do help, but not a necessity .
I talked to somebody at Mobile Dimension a couple of years ago and they do have crown in their track.Our mill has 3 10' sections of track and I was told a person could add more crown to the track by adding thin shim stock between the top of the track where the sections bolt together.
Our track has crown but when the saw slides down to the middle of the track,the saw drops 1/4".So when setting up the bunks,it's important to measure heights for the bunks off of the bottom edger.
Yes, on your question of crown and what Paul said on the bunk issue. If you do not allow for that issue you can introduce your bottom edger blade and main blade to a bunk section. :'(
Quote from: Paul_H on October 01, 2005, 10:08:28 PM
Our track has crown but when the saw slides down to the middle of the track,the saw drops 1/4".
WOW.............is that the same as saying the beam has 1/4" of crown? If so, it would seem that as the cut starts out, the crown gradually decreases as the saw aproaches the center of the beam and then the crown increases again as the saw aproaches the other end, all the while cutting a straight line. smiley_headscratch
I reckon so, as my lumber is pretty straight and true. :)
Sawmill John, could easily correct us all, as he was their main engineer for 15 years. I believe that my carrage weighs in about 400 plus pounds. I would have to read the book and I do not rightly know where it is as this moment. Most likely in the mill building, some place. ;D
Yeah,it's a head scratcher but it works as long as you have your bunks set right you will never notice.My old mill has a lighter track than the newer models like Frank's.There is no where near 1/4" of crown on our track but there is the full 1/4 " drop in the center and then it climbs back up the other side so it's basically 1/4" in 13' because our old mill can cut around 26' lengths.
When I can get the DanG thing started :D
Quote from: Paul_H on October 01, 2005, 10:08:28 PM
Our mill has 3 10' sections of track and I was told a person could add more crown to the track by adding thin shim stock between the top of the track where the sections bolt together.
So theoretically, (boy I like to say that word) since the crown is induced by shim stock in the joints, it's not a arched radai crown but rather 3 segmented segments of straight lines?.........theoreticallytheoreticallytheoreticallytheo .........
I'm a logger so I think that theoretically ;D the best way to put crown in your track is to build it straight as possible,then park your car on top till it sags and then flip it over and start sawing.
I just remembered that there is another crown(?) in the track that bows away slightly from the log to compensate for the pull of the edger toward the log.
Don't get discouraged because it's not something I've seen by looking at it,just been told by someone at Mobile Mfg
Quote from: Paul_H on October 01, 2005, 11:27:56 PM
I just remembered that there is another crown(?) in the track that bows away slightly from the log to compensate for the pull of the edger toward the log.
Brother!! .............This ain't working out quite like I wanted it to. Two crowns to preset. smiley_dizzy So how does Lucas and Peterson do it? Are they that light as to not need a crown? I've seen that shakey frame cut true in spite of crown, both top and to the side. Don't understand.
it is a very slight crown,not something you would notice and you were right when saying that the crown is induced by shims.I think MD built this right into their track but shimming wouldn't be a big deal.
Don't get discouraged,have a good look at DanGs track.
Woodbowl, your problem is solved. 8) Just weld the truss up and don't worry about the welding stress. When it bows in two directions, you will know what side to put up and what side to put out from the edger blade. ::)
Pigman, I'm afraid that is the ironic truth!..............Another unwelcome happening would be, take for example the brand X, the frame is made from 3 1/2" X3 1/2" I think. If it is not level, in a crown up or crown down and the boards are cut vertical, that would cause all the boards to be cut the same curve as how the frame lays.............huh?
WB, while yer gittin' all fancy and everthing, why don't ya just build a mill ta where you could just adjust the crown to suit yer needs? ???
I wuz thinkin'.....if you were to suspend the saw beneath the beam, rather than over it, you could put some bracing on top, sorta like a suspension bridge. That might stiffen it up enough to prevent track bounce, too.
DanG, building sections and using shim stock to create crown is tried and proven. It will work!
Quote from: DanG on October 02, 2005, 09:28:11 PM
if you were to suspend the saw beneath the beam, rather than over it, you could put some bracing on top, sorta like a suspension bridge. That might stiffen it up enough to prevent track bounce, too.
I've been thinking about that too. Can't say that I've ever seen it before. To get rid of more and more bounce, it would seem to me that you need more and more thickness of truss. Kind of a give take sacrafice when building a small mill.
Anytime I have to build something like that and bigger than my welding bench, like a flat deck truck body I use a set of steel sawhorses with adjustable feet that I made up.
Each sawhorse is 10' wide and has a 12" wide top, they were made from a single 20' I-beam that I cut in half and put legs on.
By levelling each sawhorse in both directions, and level with each other I create an artificial flat, level surface 3' in the air. My back is much appreciative of doing it up high that way during fabricating, as opposed to working on the floor. By clamping the work firmly to the sawhorses, then tacking and then stitch welding it all together you can end up with a surprisingly square & true finished product.
If sagging will be an issue it would be fairly easy to put a pair of stub legs under the center and then run a cable and turnbuckle on each side, from each end, down under the leg and back up to the other end. Tensioning the turnbuckles would force the center back up into a level position. If sideways sway and sag were a problem just use one single stout leg in the center of the underside. Then the cross-wise cables would keep the whole frame straight & true under load.
You might even be able to get away with a lighter frame by tensioning it this way. ::)