[OP]
Contributor
i have a wide belt with a steel drum and a platen. my thinking has always been to "use the platen for final sanding." recently, a friend told me "no, use the platen for all sanding, except the final pass, which should be the drum only."
what's the science and thinking behind the correct approach? ... and what's correct?
thanks,
-- dz
Contributor
I am not an expert on WB’s but was instructed to always use the platen, no matter the task. If you think about it, a WB with no platen is basically a glorified drum sander. Most of the shops I worked with just switched back and forth between felt and graphite platens, depending on the job. I realize this isn’t a clear explanation to your question but using the platen is pretty much SOP in the industry.
Erik
Contributor
curious what the logic is behind drum last pass. A drum is one small contact point compared to a platten. Wide belt i have is a drum. Other than for thicknessing my stroke sander blows it away.
Contributor
The platen is for finishing passes. It lengthens and softens the scratch pattern but runs hotter. Drum only is more aggressive for rapid stock removal.
[OP]
Contributor
thanks - this is consistent with my thinking as well. guess my friend was wrong.Originally Posted by Kevin Jenness
-- dz
Contributor
The question is easily tested. Take a moderate cut with the drum, lower the platen as you go and watch the ammeter climb. Now take off an equal, light amount of material sufficient to remove the previous grit scratch pattern using the platen on one sample and the drum only on another. See which one sands out more easily with a random orbit finish sander.
A wide belt without a platen is not a glorified drum sander. The belt runs much cooler and loads up less because of the belt length and oscillation, plus grit changes are far faster and easier.
Contributor
not really a wide belt with a drum is still a wide belt, it has a belt. A drum has the paper wrapped around the drum and is mickey mouse. The natribom also oscilates. Old quality machinery Italian stuff. Takes seconds to change the belt.
They are referred to as calibrating machines more than sanders which is logical as they do that better than sanding.
Last edited by Warren Lake; 07-09-2022 at 3:40 PM.
Contributor
That goes against everything I have learned from widebelt sandpaper manufacturers (sia, vsm, uneeda, klingspor) and widebelt techs, (scm, viet) and research on my part. Essentially platen is for finishing 150 and above, drum is for removal 120 and below. The drum leave short scratches which can effect finishing especially when staining. The platen extends the scratches minimizing andy finishing issue from the widebelt.
The platen shouldn’t take of more than 0.002 and the platen needs the proper density of felt and that is around 65, (SCM spec is 68) if you go harder you will potentially transfer belt slice marks (aka chatter). I use 26S1 felt which is 55-65, when you glue it to the platen (the metal part) and before you put the graphite on you need to calibrate it through the sander with 100 or 120 or 80g and an angle of no more than 10-12deg (so it doesn’t flip over) this insures it is parallel. There is also a correct thickness but it is machine dependent so check that. The graphite i use is PEC 500, you can use any but the 500 does not transfer graphite to the belt.
As far as belts go, there are different joints and typ have to be requested or you will get the standard “t” joint, that is fine on the coarser belts (120 and under but not great on 150 up especially if you have a steel head like i do. You want cloth on 120 and below and paper on 150 up, on the paper you want to request a “zero tolerance” joint to minimize belt splice transfer (chatter). My first choice for belts would be SIA but it was difficult to buy from them and lead time was out of control I am using Klingspor and the customer service is great and their paper is good. Sandpaper is like beer, life is to short to sand with crappy paper so don’t cheap out…
no most of this is purely “by the book” kinda info but i like to have a baseline as a starting point and adjust based on experience, machine ect…
Also there is a min and max to sand and to remove previous scratch otherwise you are wasting time and sandpaper…but thats a whole other can of worms…
Last edited by Mark e Kessler; 07-09-2022 at 5:56 PM.
Contributor
the wide belt i have only has a drum. Thats why Ive seen it referred to as a calibrating machine. It lines up to what you said about the drum only I was pointing out that it is not paper wrap on the drum, that belt changes are fast and it oscillates. Steps up from Drum Sanders. I bought it specifically to thickness on one job when material came in over spec. I only tried it for sanding once or twice.
Contributor
A steel head like the one i have (sandya win) is marketed/sold as a calibration sander were as rubber heads are sold as finish sanders but the rubber on sandya’s of this era (2000’s) are 85 durometer, nearly as hard as the steel heads. Ideally you want a max 75duro for a finish sander. Going further , a 2 head - 1st steel, 2nd rubber(75duro max) with platen (a combi head) or variations of that work well
Contributor
Yes, drum for calibrating and platen for finishing in higher grits. But there are many exceptions to this rule. For example when sanding dovetail drawer parts before dovetail joinery I don’t use the platen because it can have a slight rounding effect at the edges that can cause joints not to close. You will also find a lot of controversy about drum vs platen among pro shops. Some claim they get a better scratch pattern without the platen. This is only true if you have a rubber roller. With a steel roller probably better to use the platen. Multi head machines usually have steel first roller then rubber second and third heads. Also with different hardness.
when they first set up my Kundig they said paper belts were the best way to go. In practice this did not work well for us. The paper is very fragile and we were going through belts before they were worn out. Also if you have a single head machine and changing belts the paper will not hold up. I Started with SIA paper but use Klingspore cloth with paper on the last head because it never gets changed. In solid wood the difference between paper and cloth is very slight. Solid wood sanding is very forgiving but if your machine is veneer capable the paper selection and setup can get very technical.
Best to experiment with your machine to see what works best for you.
Last edited by Joe Calhoon; 07-09-2022 at 8:23 PM.
Contributor
the natribom has a rubber head and is considered a calibrating sander. Seen it written a number of times.
German company had me on cloth belts on the stroke for many years. 3M switched me to paper on the stroke they were fine. There is no constant pressure on a stroke like on a wide belt. The belts are also longer at 310 inches on that machine so for both reasons run cooler. I never tried paper on the wide belt, it didnt make sense that it would be strong enough. 3M cloth on the wide belt. Went from cloth to paper on the edge sander and that worked fine as well.
Contributor
on a stroke you hang your clamped up drawer off the table and sand it after its glued up and dry. Works very well.
Contributor
I ran a stroke for years Warren. Great for the outsides after assembly as you describe but not good for the inside because they are not calibration machines. They take a lot of real estate and would have kept it if more space.
Contributor
always sanded the insides first no issues. You control where you put the pressure. If the inside was rounded off on the outside edges on a stroke then its operator error. Yes 12 feet of space but can do stuff wide belts cant.
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