we do a lot of solid wood glue ups and still flatten them with a simple, 37" wide belt sander. 80g paper takes a significant number of passes to get the product flat and to final thickness. we're typically talking about removing an 1/8" total (not in one pass).
i'm not that familiar with planer sanders but was turned on to them and would just like to know more about them.
really only one question - how little can the planer take off in a single pass? we're trying to get rid of 1/16" per side but won't want to lock ourselves into taking all of that in one pass (per side). could it take a 1/32" -ish off both sides in four passes total (without showing feed/segmented roller marks)? either amount would require a more passes with our current wide belt and i'm just trying to increase this part of the operation.
any shared experiences planer sanders (and with manufacturers names/brands/models) would be greatly appreciated.
We have a 37" planer sander and can take as little off as we would like. Want to remove .005 or .010.....no problem. At that light of a pass the sander is removing most of the material. We have 150g on the sander. We've been told we should use 120g but 150g works for us so we use it.
A quality planer sander can take off 1/16 per pass easily and leave a very clean surface. I have set up hundreds of them. Avoid cemco like the plague. The closer your hold down rollers to the planer head on the in feed and out feed the better for positive feeding. Cemco has a huge distance between hold downs.
I recommend 120 grit minimum behind a planer but 100 or 80 is better.
i've since rethought my plan (after checking prices on 43" planer/sanders) and am considering upgrading our widebelt.
our single head is a 1998, and while it has performed admirably, it wasn't tracking two days ago so we brought our work to a cabinetmaker friend of mine. we helped him run our material through his new, 43" scm, two head sander. wow! not even considering the increased width capacity, the difference is night and day. we probably ran it through in half as many passes and the finished surface is unbelievably better (our panels are 35" x 120"). it then probably took us a 1/3rd of the amount of time to random orbit sand to prep for finish.
he had 80g in the first head and 150 grit in the combo head. is this normal? he uses it for cabinet doors.
so adam, thanks for contributing, i always enjoy your comments - would a two head machine really address my needs (primarily, increasing the speed at which we can flatten to dimension - taking an 1/8" off total, and decreasing the amount of time we random orbit sand), or am i just seeing the benefits of a new machine, and a single head would yield similar results. for the first time, i'm leaning heavily towards a new machine and there is a significant price difference between a single and two head sander.
I would recommend you read my article on the SurfPrep sanding website on 2 head wide belt sanders. If you spring for an SCM, which is a great machine by the way, I would get one that has air exclusion on each of the three sanding contact points. This means you can retract either of the drums or the platen instantly.
The first drum will be steel for cutting things flat and planing. The drum in the combination head will be 40 shore for a longer more shallow scratch. The platen in these machines is usually 50mm wide (2").
80, 150 not a good sequence but it's not far off.
Running a part through the same grit sequence is actually not a very good idea. If you sand a rough surface down to 150 grit the scratch is only a few thousandths of an inch deep. When you do a second pass on the same surface removing the same amount of material, the second pass is removing solid wood. Maybe up to twice the actual mass of wood is removed from the surface.
It is very important to not only knock the surface down flat, but also to leave a proper scratch pattern for the finishing sequence to remove.
I would much rather see you run a 100 - 150 finishing sequence. Use at least a 60 grit by itself on just the first head to knock it down flat on a few passes and then use the 100 - 150 to remove .015" to get rid of the 60 grit scratch.
This is a real quality way to get your job done.
If you leave .015" per side to finish, you have .095" of your .125" left to remove. Even with a smaller SCM you should be able to remove that with 3 passes at 60 grit.
The reason this is important is because the final grit sequence will be removing a scratch pattern, 50% of that is air. The final sequence will be under very little pressure so the belts will run a very long time. Your color for stain will be excellent and reliable.
This is a lot to take in so feel free to send me an email and we can discuss this in person.
thanks for the reply, and offer for further assistance. i think i understand what you are saying but will keep you offer to discuss it over the phone in my back pocket.
we've been using an 80g belt to level, followed by a 120g to remove the 80g scratches (and ease hand sanding). unfortunately, we're still left with significant scratches and i've followed your article as best i understand it. we'd tried adding a 100g in between but we haven't seen a difference so we skip that now. swapping belts on a single head machine isn't that fun to begin with.
our machine typically wants to scream and shut down if we try to take more than .01 off per pass (depending on width). this is what we do for 80g and usually .005 for 120g. we've experimented with taking less than this off and/or lowering the platen to improve scratch pattern/depth off the machine with no real results. i have thought it was just how the machine operates but after experiencing a new machine - i ready to make a change. i mean, we probably only average 10 hours/week on the wide belt and 20 hours in hand sanding. the results, as they appear to be with our new machine experience, would likely cut both numbers in half. this would make it pretty easy to justify a new purchase.
are there any other features that would be beneficial? the operator of the scm (i was just catching the parts) said something about an air bladder platen but i wasn't fully sure i was following him.
Air bladder platens are not required. They are good for fine finishing. The SCM machines put out a quality finish with a regular platen.
The air retraction on each head is a big deal.
Do the belts need tightened on the machine you have now? It shouldn't scream on a .020" pass in any quality machine. Only use the platen on the last pass. If you want to know if your ugly scratch is an artifact of the 80 grit then just angle your panel on the last pass. If you see short uglies running angled to the direction of the feed they are 80 grit scratch.
80,120 on a two head is not a bad option. You can still use the 80 by itself on both sides and finish with both heads.
One advantage of just using these two grits is that you can run paper on both heads all the time. Paper has a much flatter substrate and the scratch is far better. Less hand sanding with the same grit sequence. Belt life is huge when you do it right.
There are many ways to skin a cat. My job is to help you find the best one.
SCMI and Viet both stand out for machines with air retraction, easy adjustment, dead shafts for smoothness and rigidity, and proper configuration. I have seen some SAC machines that don't look bad.
The taiwanese machines are okay but they will never touch the two companies above for quality or finish. It is very rare to see one with retractable heads and it will be poorly executed. The drums hardness is rarely properly executed either.
The other brands have odd issues that are unique to the brands.
One German company makes machines in this size range but they use solid steel hold down rollers and a very soft conveyor. Snipes on narrow parts are nearly impossible to avoid.
Same company is enamored with super hard drums in inappropriate places. The buyers of these machines don't know these things will bite them in the butt later.
A Swiss company making machines in this size builds their combination heads about 6" wider than necessary making driving parts through less than 18" without back up slightly iffy. No reason for it other than stubborness. At least he stopped using 85 shore rubber drums in his combi heads after I talked to him.
One thing to keep in mind is that the SCM was sanding down to 150g, granted it was not ideal by following an 80g head, your sander was sanding down to 120g. Huge difference when it comes to finish sanding.
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