I wanted to get some opinions as I have only my limited experience to draw from. Iím looking at a couple of options for a new widebelt sander for our operation (and new to us - we'd get a used machine). Iím trying to decide between a single and two head machine, and between a steel and rubber contact drum/roller. Right now we run a 36" SCMI with a combination head. The contract drum is 4-6" steel and the platen is felt. We use it almost exclusively to dimension solid lumber glue-ups. These glue-ups vary in size but are typically table top and larger. We run an 80g cloth belt with the platen up until we get a flat surface. Push the platen down and, sometimes, switch to a 120g belt to help with some of the scratch marks. From there, we random orbital sand with 80, 100, and 120 to remove widebelt sanding marks before we do finish work. The random orbital sanding is time consuming work.
1. Would a single head, rubber contact drum/roller be better, worse, or the same vs a steel head (for our operation)? Achieving a flat, uniform surface is of prime importance.
2. We're looking at a machine with an inflatable platen. How does this compare to a felt platen? Would it do a better job at removing scratch marks left by the drum? Would it work on solid wood, or is the benefit only for veneered work?
3. If we stepped up to a two head machine, is it customary to run one head more than the other? We'd only run the first head to dimension and make flat and then run both on the final couple passes. Is this how this is customarily done?
4. How much does horsepower matter? We're typically gluing up 1/8" over-sized and then removing .01" per pass. This means approximately 10-12 passes to achieve final thickness. Our current machine is 18 hp and not capable of removing much more than that in one pass (with an 80g belt).
From Contributor O:
It is time to talk to an abrasive salesman. I just love that term. Yeah really, aren't they all? But seriously, if you are removing .125 or so, you should be using an abrasive planer, and yes it will be higher horsepower. You should get the job done in two passes, one each side, then on to a finish sander, perhaps your single head with a platen would be adequate. Ten-twelve passes is a lot, a whole lot.
It has a steel first drum for calibrating, rubber second drum, and a felt platen. The drums pivot with air cylinder actuators, so that it is fast and easy to activate and combination of drums and platen from the control panel. It is simple to run a rough pass with just the first head, then a second pass with two or three contact points. We standardized our grits and leave it set up for an accurate thickness reading off the second head. If we do go to a coarser grit on the first head, the readout is close enough because the belt is a bit thicker.
Using just the drum on the planing passes is exactly right. Even if you get a two head I often advise to only use the first head since it is often very hard or steel. If you upgrade to a two head buy quality. Buy a drum, combi-head machine. I could write a book on why this configuration is better most of the time. None of the Taiwanese machines have air exclusion like a SCMI or Viet. With air exclusion a flip of a couple switches pulls both the drum and platen in the second head out of the way to protect them while you are abusing your first drum only. Air bladder plattens are nice but not great for the coarser work you are doing. They offer no real advantage and they do have issues with dry rot and leaking. The medium density rock hard felt that the better machine companies use is much better for your job.
If you set yourself up with a good two head with at least 25 hp on the first and 15 hp on the second you should be able to slow your feed down a lot and take a few .025-.030" passes with a 40 grit cloth. Cut the part to .040" over your final thickness. Switch that out for a paper 80 on the first head and paper 120 on the second head. Sand .020" per side and you are golden. Maybe 5 passes total. Hand sand with 120 grit and your sanding time should be very short. There is a trick to it though.
Planer sanders are great and a curse at the same time. Finding a well-designed one for cheap is very hard. Hold down rollers should be as close to the cutting heads as possible. There are cemco planer/sanders out there with 3ft between hold down rollers. Who thought that was a good idea? Timesaver does a good job on this. If you buy one get two sanding heads after the planer head. Run a minimum of 100 grit (better an 80) on the drum and 120 or 150 on the combi-head. They are not cheap but this configuration will give you one pass per side and light hand sanding.
Timesaver made machines for years with 75 shore drums on the first head. I believe this to be a bit too soft for a multi head machine, but it is not terrible for a single head machine. 75 shore will cut plenty, but it is not going to produce the flatness of a 85-90 shore drum, or a steel drum. A softer drum will most definitely make a shallower scratch pattern. All of the features you seek in a single head machine are tradeoffs. A harder drum will cut flatter, but make scratches much harder for the platen to remove. A bladder platen will give you precise control over stock removal, but it will not remove enough material if you are trying to push your platen slightly beyond its design limits.