Hi folks, I’ve been using baltic birch now for decades and sometimes think to myself that I know a lot about it’s properties and all kinds of techniques to get good results machining it and also finishing it. But it’s times like this that I feel clueless! I need your help if you know a thing or two about either or both of baltic birch, and/or drum sanding. Your thoughts on this would be very much appreciated!
I continuously have to process multiple skid quantities of baltic birch parts and am always looking to reduce the manual labor and/or increase the quality of the outcome. Recently I decided to put a dual drum sander into my manufacturing runs. I went out and bought a used Craftex B2022 24” dual drum sander. I commissioned the drum sander by cleaning it up, doing general maintenance and then squaring the drums. With the drums squared to feeler gauge accuracy I am still getting drastically uneven and unpredictable results. sanding through layers in some places. I have quadruple and quintuple checked the drum alignments. They are bang on parallell with the bed.
I have moved on to scrutinizing the parts themselves and I think the universe is trying to force new information into my head (-it’s a very difficult experience as I’m sure you can imagine ). I use almost exclusively 9mm 5x5 BB/BB. I buy it in multiple skid quatities and store it flat on my shop floor. I get the odd warped sheet but generally ita all pretty flat and usable. What I think I may be seeing in this case is a kind of warpage you can’t readily see on the scale of a sheet. When a sheet is warped, it’s not really a big deal as long as your hold downs on your CNC are good. I don’t have any problems with he sheets on my 5x10 machine. Putting the cut out parts through the drum sander is a different story though. I’m finding what I think is “higher frequency/shorter wavelength” warpage. This warpage makes for highly rigid peaks and valleys in the smaller machined parts. So the rollers and drums apply down pressure on the parts but for these short wavelength warps are not flattened out by this pressure.
My question is: What do you think about that? Am I on crack here, or do I just maybe have a few skids of a “bad batch”? or do I have to learn that a drum sander is just not a suitable machine for sanding 3/8” baltic birch parts?
On a side note, I have tried Amana’s “non-random orbital” CNC sanding disk setup. It worked well. This entailed sanding both sides of each sheet on the machine, prior to machining the parts. It works okay. It increases your machining time a little more (IMHO) than it reduces your time sanding by hand with a random orbital. When I tried it I had a 4” sander because that was all that they had. Amana recently released a 6” version. I want to try that. Problem is that they are REALLY expensive. I’m kind of nicked that the 6” one came out only weeks after I bought the 4” one. If I had known I would have waited.
Anyway, It’s been a long time since I’ve been here on the forum. Nice to see you all again and “hello” to all the newbies!
When you look at the places where it has sanded through, is it the same thickness as the places that haven’t sanded through? In other words, does your Baltic birch have high spots?
No, it’s thinner in the places that are sanded through. And when I inspect it on my (flat) table saw surface I can see the small warpage. The thinner areas are raised up from the flat surface. these “warps” are up to a couple mm in height and span up to several inches. Inspecting the parts where this is occurring its all over the part. The small curves are quite rigid. It’s not like what I’m used to seeing: It’s very common to see a minor bow or twist in the part that spans it’s length and when you just press gently on it it goes flat. These “micro warps” I’m seeing are as strong as skateboard concavity! I’m guessing most people don’t use a drum sander on 9mm? It might be that it’s just not the right machine for the job. Maybe a brush or flap sander…
These are definitely good troubleshoots. I hadn’t thought about checking the drums for consistency in parallel across them. I used 1-2-3 blocks on each end with feeler gauges. I’ll have a look at that.
The sandpaper I’m using is something I question .I ordered it from Amazon. It was listed an “cloth backed sandpaper rolls for drum sander”. I was disappointed when it came because it was actually backed with hook/loop backing. The kind of backing you’d want if you were cutting your own sanding disks for a hand sander. So the backing is kind of soft and a few mm thick. I’ve ordered the right stuff from Klingspor. Maybe the right paper could make a difference.
No I don’t think you could just sub in a 6” disk. It doesn’t just spin, it orbits as well. It has a counter weight built in to it and it’s balanced for the 4” disk. I bet it wouldn’t hold together for long if you tried that that.
I do have some larger stock kicking around the shop. It’s a good idea to see how it performs on some 3/4” birch ply, and some 8/4 boards . I’ll definitely check that out.
My only justification for a machine like that is for a product I make that uses exclusively 9mm. Once I solve this problem, if I find that It’s not the right machine to process 9mm baltic birch, I’ll have to list it.
How long are the parts you are running through the sander? You are running parts through the sander to take the burr off the cut edges or improving the face sanding more than the factory finish from the sheet? Does the sanding sound smooth or hearing some chatter? Same grit on both drums? I could see the loop backing causing some chatter problems on a drum.
The parts range from 36”Lx30”W and smaller. I’m running the parts through to bring the face surfaces up to 180 grit. I have 150 on the front drum and 180 on the rear drum. As far as the sound goes, I’m not hearing what I’d characterize as chatter. It sounds as I would expect but then again I haven’t used drum sanders enough to think I know what they should sound like. I think youre on to something wrt the backing. My plan right now is to set the machine aside for a while and wait for the correct sand paper rolls to come in. I’m going to order them from Klingspor. I wish there were stores in my area that carried this type of stuff. For now I’m going to have to finish the run I’m working on the old fashioned way.
Yeah it’s interesting. I also wouldn’t put a 4” on one that’s made for a 6”. The balance would be just as bad. I checked out the one you have. It’s a lot less expensive than the Amana one (like half the price). If I do get a 6” I’ll go for that one. Thanks for the tip!
). I use almost exclusively 9mm 5x5 BB/BB. I buy it in multiple skid quatities and store it flat on my shop floor. I get the odd warped sheet but generally ita all pretty flat and usable. What I think I may be seeing in this case is a kind of warpage you can’t readily see on the scale of a sheet. When a sheet is warped, it’s not really a big deal as long as your hold downs on your CNC are good. I don’t have any problems with he sheets on my 5x10 machine. Putting the cut out parts through the drum sander is a different story though. I’m finding what I think is “higher frequency/shorter wavelength” warpage. This warpage makes for highly rigid peaks and valleys in the smaller machined parts. So the rollers and drums apply down pressure on the parts but for these short wavelength warps are not flattened out by this pressure.