parallelogram for up and down movement?

Satamax · September 22, 2011, 06:06:34 AM

Hi everybody.

I would like to use a parallelogram on the same idea as in this video

http://www.youtube.com/watch?v=ZpBEHnge41M

To raise and lower my bandmill saw head

Anybody can see a point why not?

And on a side note, how much side to side pull is tehre when sawing? And if the saw moves a smidge is it bad? Or does it have to be absolutely rigid?

Thanks a lot and best regards.

Max.

redbeard · September 22, 2011, 12:24:11 PM

I always liked this kind of idea. I had plans of making something like this setup for making cants to fit my mill. You are really taking on some engineering. It sure would be nice to have that kind of contol you could mill almost any curved log for some nice natural arches. Keep your ideas going I like this concept.

Satamax · September 22, 2011, 12:35:00 PM

Hi Redbear.

Thanks a lot for your reply. Well, i didn't mean anything like you showed.

You se the diamond shape of a pantograph?

That's what i meant, two of theses in a vertical plane, to adjust the height of the bandmill relative to the track. Instead of screws or cable, chains etc! A pair of parallelogram and an hydraulic ram. I'll try to do a sketch later.

york · September 22, 2011, 12:54:50 PM

Max,this is an interesting concept,but think about all the weight,you will be putting,forward of the head-you would have a rather long wheel base on the head in order to make this work-not sure i like it..Bert

Satamax · September 22, 2011, 03:29:56 PM

Hi Bert.

Well, the idea would be to atach the saw via the parallelogram onto this.

http://www.agriaffaires.com/occasion/tracteur-enjambeur/1893971/braud-1014.html
It's a 90 HP grape picker with it's picking head removed. All hydraulic. I would be driving the wheel of this

With the hydraulics, and also power the up and down ram.And obviously the feed would be done by the wheels.

I have some mine chariot wheels.

Last thing to find, railway wheels. And cheap transport for the tractor.

Satamax · September 22, 2011, 11:34:22 PM

Hi guys.

Well, please forgive me for the crude toshop sketch.

kelLOGg · September 23, 2011, 05:53:24 AM

The sawhead path will be an arc with this arrangement not a straight line. I don't know if that is a problem or not.
Bob

Satamax · September 23, 2011, 05:56:56 AM

Well, as long as the band is horizontal and the saw vertical, i don't see a problem myself, that's why i asked. If someone knew better than me.

Ianab · September 23, 2011, 06:01:27 AM

Quote from: kelLOGg on September 23, 2011, 05:53:24 AM
The sawhead path will be an arc with this arrangement not a straight line. I don't know if that is a problem or not.
Bob

It may limit the max size log than can be sawn as the head will move horizontally.

But as the max reach will be when the head is horizontal, and in the widest part of the log, then this may not be such a problem.

But it will reduce the cut width at the top and bottom of the range. Only an issue with large logs of course.

Ian

kelLOGg · September 23, 2011, 06:05:35 AM

The parallelogram idea is how I get my lumber to the kiln. To use this idea for placing a band for the next cuts throughout the log would require very accurate engineering. Interesting concept - go for it and keep us posted.

Brucer · September 24, 2011, 12:21:57 AM

The principle is fine. There are some issues you'll have to allow for.

1) Side-to-side stability. You will need to seriously stiffen the arms in the lateral direction. Diagonal cross bracing between them would be great except there'll be a DanG log in the way. If you don't plan for this you will have the potential for the blade "chattering" in the cut.

2) The bushing or bearings on the pivoting joints will have to have a very small clearance. These joints have the potential for a lot of wear. Since that will increase the clearances, you'll need to have a reliable way to keep them lubricated.

3) Geometry. As you've shown it in your sketch, when the saw head is very low there will be a lot of pressure on the cylinder. This suggests either a crank at the base of the lower arm, or moving the base of the cylinder out in front of the support.

4) Torsion between the linkages on either side of the log. You have to be certain that one side cannot move up or down ahead of the other side. Otherwise your blade will not be parallel to the bead. The lower the sawhead, the more likely there will be uneven forces trying to force the head down.

None of these is a game killer. Deal with them at the planning stage and be prepared to make revisions after the first test run.

Satamax · September 24, 2011, 02:40:37 AM

Hi Brucer.

Thanks a lot for your reply.

I was playing with the idea of using a st andrews cross in between the two top arms. May be the bottom ones too, as i can atach to the top third of the saw only, or a bit more. I didn't think pivoting points would be that critical. But i was thinking about ball bearing pillow blocks.

As for the ram, i don't see what can do any harm to hydraulic rams! I was thinking one each side, exact same ones, slaved to each other, i mean paralleled.

Still, the pivoting points bug me. Ball bearing pillow blocks are costly. i'm cheap hey! :D

eastberkshirecustoms · September 24, 2011, 04:02:24 AM

It may not be an issue, but my concern would be the distance between the blade and log changing when you raised or lowered the head. -EBC

ladylake · September 24, 2011, 04:59:32 AM

I'd keep it simple, 4 post straight up and down. Steve

Satamax · September 24, 2011, 05:23:39 AM

Hi guys.

EBC, this is a concern when the log is close to the saw head. No doubt it could lead to problems. I'm not going mobile thought. So if my friend working for the french railway can shift is rear end, i'll have long enough rails.

Steve, what if it's not simpler?

I want to atach it to this.

http://www.agriaffaires.com/occasion/tracteur-enjambeur/1893971/braud-1014.html How would you arange the four posts?

Thanks a lot.

Max.

ladylake · September 24, 2011, 06:44:08 AM

What is that? I'm guessing you want to mount a bandsaw on the side of it. Looks real complicated and I'd think the head would bounce up and down mounted out there, It might work good for splitting big logs where you wouldn't have to be real accurate. Steve

Satamax · September 24, 2011, 09:48:22 AM

Hi Steve.

Well, it's a grape picker. It's like a pig portal axle tractor even bigger. The space underneath might be 5 or 6' high and about 42" wide. And the idea would be to mount the saw in front. It's a 90 horsepower hydraulic drive, and feeds the pumps etc. I'm thinking of powering the saw with the hyds too. I have mine cart wheels which gonna go in between the actual wheels lenghwise, which will run on railways. The tractor wheels will be only touching the rails slightly to proppell the thing. What would be huge, is if in the future i can have a slab of concrete flat enough so i can cut crucks with it ;D Better idea to go mobile with it would be to have a follower, i mean you start your cut with a laser line on the side of the log and it would follow it. I know it's possible, but it's out of reach for me, as i'm not clever enough. This would permit cutting in a field or on a car park.

york · September 25, 2011, 11:36:41 AM

Max,your concern about side to side and make it rigid-you could weld in a cross tube,close to the pivot point,of the lift arms,kinda like what John Deere does on there FELs-you may be on to something here,Bert

mikeb1079 · September 25, 2011, 02:56:17 PM

mr max i don't want to rain on your parade here as you have some good ideas but it seems like your bent on reinventing the wheel. there's a reason why all the bandsaw mills have a similar design: it's simple and it works. why not use an established design then adapt to your specs?

Satamax · September 25, 2011, 07:08:40 PM

Hi everybody!

Well mike, just explain me in what it is simpler to use a four post, two post, chain rack and pinion, cable winch, cantilever head or whatnot, than my system? I want to atach it to a grape picker, because it's all hydraulic, it has enough power to power the saw head. It already has forward and reverse motion built in. I have most of the parts either on hand or spoted. So what would you do, put a four post with the chain in front of the tractor? I haven't said it's either all decided, or on the way to completion. Some projects take more time than others.

And if they weren't people like me trying to adapt, refine, modify and all this. You would still be hunting with wooden spears, may be with a stone on the end. But in it's time it was already a revolution!

Hilltop366 · September 25, 2011, 08:01:05 PM

Hi Satamax, interesting project you have here.

I'll weigh in on the discussion, as long as you keep in mind that I don't have the saw parts in front of me and have never seen a grape picker other than the picture in your link.

My first thought about the parallelogram is that it puts the saw head further out of the grape picker and would magnify any change in the difference in the height of the front to back wheels as it is going down the track causing the blade to rise or dip and also make it hard to keep the blade (front to back) parallel to the track, I also think that Brucer brought up some valid points.

I think that a pair of sturdy post with a cross piece at the top and fastened to the inverted U shaped frame would be the easiest and would be more sturdy, a lift system like Bandmiller2 had described to me once that has a hyd. cylinder with a double pulley on the rod end that pushes a cable in order to shorten it and cause the saw head to lift. (think fork lift, for every inch of cylinder lift you get 2 inches of saw head lift). One piece of cable to each side of the saw head with a eye bolt for adjusting side to side height.

eastberkshirecustoms · September 25, 2011, 08:44:46 PM

Quote from: Satamax on September 25, 2011, 07:08:40 PM
And if they weren't people like me trying to adapt, refine, modify and all this. You would still be hunting with wooden spears, may be with a stone on the end. But in it's time it was already a revolution!

I'm not trying to offend you, but your tone comes accross a little defensive toward criticism of your design ideas. You did ask the members 'why not',

Quote from: Satamax on September 22, 2011, 06:06:34 AM
Anybody can see a point why not?
Max.

so they (we) are responding as such.

I commend your thinking outside the box, I too, like to stray away from mainstream, but when something works, it works and you go with it. I feel that the guys here want you to succeed in your project and are just trying to keep you from setting yourself up for failure.
On that note I say just go for it. If you pull it off it will be one bad ass and unique mill, for sure.
I just know from experience that redesigning something that doesn't work after putting many hours into it really sucks.

beenthere · September 25, 2011, 09:18:37 PM

eastberk.......

That was a good and fair summary of what the responses to Satamax have been....IMO.

Brucer · September 25, 2011, 11:50:01 PM

Quote from: Satamax on September 24, 2011, 02:40:37 AM
As for the ram, i don't see what can do any harm to hydraulic rams! I was thinking one each side, exact same ones, slaved to each other, i mean paralleled.

When the ram is fully extended, the backward force on the sawhead will be magnified considerably when it reaches the ram. This will apply much higher forces on most of the rotating joints. This in turn will magnify any "play" in the various joints.

When I'm trying to drive a linkage with a hydraulic cylinder, I determine the midpoint between the two extremes of motion. Then I try to arrange for the cylinder rod to be at right angles to a line between the pivot point and the end of the cylinder rod.

Quote
Still, the pivoting points bug me. Ball bearing pillow blocks are costly. ...

Ball bearings may not work well in that application. They will only be rotating through part of a turn and will eventually wear unevenly. Lubricated bushings may do a better job.

barbender · September 26, 2011, 12:30:00 AM

I think the parallelogram idea has to many joints, you're going to have a hard time dealing with the lateral movement for one. When the blade hits the wood, it pulls pretty hard to the side. It just seems like you are doing it the hard way, but I don't doubt you could make it work. I'm all for innovation ;)