Lamination tolerance

[skeaterbait]

Quick question for all the smart folk here. I recently bought a drum sander for making lamination's, a used G0458, and I have been struggling with it a bit. After overcoming the first obstacle of it not having pressure rollers but rather pressure plates, I have been able to successfully make a couple of lamination's.

The issue with this is that they are not uniform all the way down the lamination. It's not off by what I would consider a huge amount but I don't know if a finished bow would have the same idea of acceptable as I do.

So, on to the actual question, will a variance of .002-.005" make that much difference at the end of the bow build?

I am guessing that the variance will be in my sled more than the sander but since I made it from 2 pieces of 3/4" plywood glued together I can't really run over the jointer.

[kennym]

Lonnie,

If it has a conveyor, try not to put the lam on the splice. This drove me crazy and caused me to get rid of one sander only to find the next one did the same. About .004" difference randomly somewhere on the lam for a little ways.

Finally the light came on and with some testing, it was the splice was slightly thicker than the rest of belt.

If no conveyor, the feed rate by hand needs to be constant.

[kennym]

Oh, and maybe the smart folks will chime in!!  

[skeaterbait]

LOL, I have great respect for your smarts Kenny. I will look for the splice on the conveyor, my fear is since the belt is fairly short and I don't know if it can be avoided since the sled is longer than the feed table.

That could account for the variance not always being in the same place.

[Roy from Pa]

I'm chiming in...  

[kennym]

The belt runs top and bottom so if you have an 18" feed , with the diameter of the end rollers you should get close to 36"

Most bows don't need lams that long  anyway .

 

[skeaterbait]

Good point. Grizzly says the belt is 44 1/2" so I would bet it's close to an 18" feed. I will definitely check it out this afternoon when I get paroled from work.

Thank you for the info.

And Roy, we appreciate your .02 as well.

[bamboo]

run the drum lightly on your belt for a spell to even it up

[skeaterbait]

This one has a sandpaper belt, not sure if that would work.

I measured the feed table, it's 21" but the seam runs diagonal and covers about 6-8" (at a guess). I will tinker with it tomorrow maybe. I got side tracked working on my form. I put a fiberglass strip on it last night and now sanding everything flat and square. I never knew how much work goes in to the form itself.

[skeaterbait]

No one has really said but I am guessing that much variance will cause issues?

[Wolftrail]

,"will a variance of .002-.005" make that much difference at the end of the bow build?'

probably not, all I know from mechanical experience is I once refurbished a small engine once. The ring gaps were at the limit after re-honing and the connecting rod bearings and crank journals were so scored you could drive through them.  The engine ran like a scared rabbit for 3 years and never died.............. drove the car to the ground on a daily basis.

 

[LittleBen]

I can't say if that variation matters, but I would just mark the high or low spots on all the lams with a pencil and when you build the bow, don't let them overlap.

It might take less time to just build the bow than to try to tune the machine. May turn out its irrelevant.

If you can measure the lam, then you must also have the technology to measue the sled. See if it is off. .002-.005 might be coming from an uneven glue line between the sled pieces.

[bamboo]

.015" is 5# in the middle of the range [40-60lbs]on my 66"longbows---so having thin spots in your limb could cause variations in performance--will make a bow ? certainly!--IMO the more you keep refining the process --the more predictable the outcome---when your grinding lams keep flipping and reversing them as you feed them--and when you are close to target thickness-.010"-don't even touch the crank--sneak up on it

[skeaterbait]

Thanks all, very good stuff to think about and watch for.

I have been messing with it and I think I found a sweet spot that comes out really close to spot on, only .002" or so variance.

For now I will give it a break since I got distracted and let my finger get pinched between the feed belt and the sled. It's amazing how much downward pressure that drum has.    

I am assumming that you ran your sled through the sander first without lams to true it up, And on both sides...  The last time you run your sled through mark it with an arrow and run it through the same direction every time...  
  Does your sander have hook and loop sandpaper...  I am not a big fan of that crap and I suggest getting rid of it and glue your paper on with some spray adhesive...

   As a side note... A few years back I made some lams unknowing to me with low spots in the middle...  Just so happens that it ended up being my fastest bow for a year or so...  Who woulda thunk...   Lol...

[skeaterbait]

I did run the sled through a few times but never thought about running it through the same direction from that point on. So at this point I have no idea which direction is which. But I have also glued some sand paper on the top to help hold everything in place.

My drum is spring loaded, so no hook and loop to worry about.

Cool that there is no hook and loop... That chit rounded the corners on my lams...
   If your machine is slightly off it will be multiplied if you run your sled backwards or flipped...  I would run it though once or twice and mark the way you ran it through and run it through the same way every time...  Mark top and bottom also...  Good luck...  I hope things start smoothing out for you...