Thickness Sander questions

[Ron Burns]

Hello everyone,

I've recently built a thickness sander using a 3 x 5 inch drum driven by a high torque DC motor. I've never used one before and was curious what speed I should be running the drum? Power is not an issue as I can get up to 48 volts at 10 amps current draw. The motor is rated to 12 - 36 V rated at 9000 rpm at 36. Speed has been cut in half by a 2:1 pulley/timing belt. The other question I had is what direction should the drum be turning? I thought I had read somewhere here I believe, that material should be fed against the direction of rotation. Any help would really be appreciated!

 

Thanks a million

Ron

[Jaager]

1700 rpm is about the max  for any of this sort of sanding machine.  I have not done the experiment, but I suspect that  mush faster will produce a well charred surface.

If the rotation is in the direction of the feed, you will have an electric motor driven version of a medieval or Roman era projectile throwing weapon war machine.

Even at your slower 4500 rpm, any stock will probably deeply penetrate drywall.  Mere human flesh would not stand a chance.

 

I suggest dropping back 10 yards and buying a Byrnes Sander.  I have experience with making my own - from way before there was any commercial machine - and the ease of use and precision with the Byrnes makes any homemade machine an exercise in pointless frustration. 

[Ron Burns]

Thanks Jaager! I'll keep those speeds in mind and consider your advice in regard to the Byrnes sander. Money is tight these days hence building my own. It actually worked out well I think but the proof is in the pudding. I need to finish a couple of things and I'll show the results. Here's a peek so far ...

Ron

Edited November 6, 2020 by Ron Burns
bad formatting

[Jaager]

The top support is way over engineered.  Cutting a hole for the Vac intake will involve a lot of work.  The back vertical face will want a piece of material - cardboard will do - that comes down for a distance of about to the middle of the drum - to make an enclosure for the drum thrown wood flour.  The volume of dust generated by a drum sander needs to be seen to be believed.  Because of my thickness sander as well as my drum sander table, I had a supply of N-95 masks when this current disaster washed over us.

A shop vac (serious volume) and an inline cyclone trap ( a serious sanding session will fill a 16 gal vac container in less time than would be expected as well as filling a vac filter in an all too short time). 

[Ron Burns]

Jaager, I'm glad to make your acquaintance! I will take your advice and re-do the top and add to the back side as you suggest. I have some 6mm ply I can cut to size. The 18mm top piece is a bit overkill. The warning about the dust is good. It will save my hide from 'she that commands'  Perhaps I will find a place outside to do my sanding. Since the big 'C' hit she's been tolerant of my messes in the apartment but now that the treatments are coming to an end I have to watch it a bit more! 

[Ron Burns]

Hi all,

Got a bit more done on the sander to the point that it functions but with a slight wobble to the shaft. If running a piece through too quickly, it will leave slight divots in the wood. I think this may have to do with not having my tension spring installed yet or...I think I made a mistake using 'self leveling' pillow bearings. Regardless of that, if I go at a reasonable speed pushing the piece through, it works with no visible divots! I got a piece of Alaskan cedar down to .6 mm and could probably go much further. I have yet to install the vacuum port and thought it wise to not make any more sawdust. In case anyone is interested, I used a 1/4-20 swiveling, self levelling machine foot as my elevation device. It worked like a charm after epoxying the base into the sander's base board and tapping a loose thread in the aluminum plate. A simple left or right turn to adjust the height and the swivel takes care of the angle increase or decrease with hardly any play at all. The motor is a high torque DC unit run on a 10A variable power supply.  As always, any suggestions or if you see any fault in my layman engineering, please feel free to comment

[bricklayer]

Ron

If you want to run the drum sander at high rpm with low vibration, then you have to balance the drum, I suppose.

There should be equal distribution of mass around the longitudinal axis. See balancing vehicle`s wheels.

The drum should be balanced with abrasive paper mounted, like a wheel is balanced with tire mounted.

Nonetheless I like your simple design that  you can modify according to your needs.

What about a conveyor belt to ensure constant feed of material to be sanded?

 

Michael

[Roger Pellett]

My home made thickness uses a 1/3rd HP 110v AC motor that transmits power via v belt.  A stepped pulley allows control of Sanding drum RPM.

 

When I first started using it sanding media life was so short that the machine was nearly unusable.  Then after reading a post on this forum I had a Eureka moment that as an engineer I should have had much earlier:  Reduce the RPM!

 

I flipped the belt on to a smaller sheave at the motor, thereby slowing the drum speed.  The thing now works like a charm.

 

Running the drum sander at high RPM is not necessarily a good thing.

[wefalck]

I don't really have any experience with drum sanders and don't really need one for my current projects - however, I would be a bit concerned for the motor life with the open commutator. Dust can accumulate in the motor very quickly.

 

I gather the life-time of the abrasive paper also depends on how much thickness you take off by pass. If the drum gets too hot, you may rip out more easily the grains. So there will be RRMs, feed rate and thickness per pass to consider.

[Bob Cleek]

35 minutes ago, wefalck said:

...., I would be a bit concerned for the motor life with the open commutator. Dust can accumulate in the motor very quickly.

 

I gather the life-time of the abrasive paper also depends on how much thickness you take off by pass. If the drum gets too hot, you may rip out more easily the grains. So there will be RRMs, feed rate and thickness per pass to consider.

 

Yes, on all counts. i can't imagine running one without a good vacuum pickup. (My Byrnes sander has and excellent one.)

 

Plain sandpaper isn't really the best option. What is the best is the same heavy cloth-backed abrasive material that belt sander belts are made of.

Edited December 13, 2020 by Bob Cleek

[wefalck]

In theory you can buy this cloth-backed abrasive in all sorts of configurations and sizes: from 1 inch wide up in rolls to the normal size sheets, from 40 grit to 2000 grit, I think.

[Gaetan Bordeleau]

I did a thickness sander few decades ago and I sold it few years later. Then I bought one  with a second motor for the automatic feed. Feeding at a regular speed will produce a more  even thickness all along the plank. It is exactly the same principle in turning. If you turn by hand, the finish is rough but if you use the automatic feed, it will be completely different and much more smoother and regular in thickness.

 

I have a 16 inches long drum and the paper used is specifically design for this application only. I change the paper around 1 time a year.  The easiest way to scrap the paper is to sand a wood like bloodwood, the particules clog on the belt and burn. I use #80 paper and always sand in the wood direction. If I would use #80 paper for a sanding disk, the results would not be good. In fact, I do not understand why peoples use a sanding disk, with a sanding belt, results will always be better.

 

If I use a too much fine grain, the paper will have a tendency to clog. For what I do, #60 would be too coarse and #100 too easy to clog, 

For Byrnes sander, I do not know which paper grade is best, because I did not tried it.

[AON]

Bonjour Gaetan

I have a combination disk and belt sander on my worktable.  I've use both regularly, the disk for end sanding small pieces and the belt set horizontally for larger flat pieces.  It has an option to flip the belt vertically.  I've never done this.  After reading what you posted I think I will give it a try and find out for myself what you are talking about.

 

It will also give me an opportunity to clean under the belt!

 

Thank you for making me wonder about it.  I am open to learning.

Edited December 13, 2020 by AON

[Roger Pellett]

For my NRG design home made sander I use cloth backed belt sander belts bought at our local home improvement store.  They seem to hold up.

[Ron Burns]

Thanks everyone for your comments and suggestions! We're getting closer to a conclusion. Now I will..

1- Get the vacuum attachment ASAP

2- Figure out a way to isolate that little DC motor. It's built like a small cheap tank but I can see it jamming up real fast with crud

3- The auto-feed seems a bit beyond my ability and most of all my knowledge. Google will help  I can see the benefit of a steady feed, Thanks!

4- Isolate that wobble! For some reason I feel it's the cheap self levelling bearings. I'll see what other flanged ones I can find. As far as balance is concerned

that drum was a solid piece of aluminum that I had bored out for the axle. There is a 1/8 inch channel about 3/16 deep to accommodate my paper which is kept in place with screen door spline ( I was proud of that idea :)). The hubs I used are milled aluminum and identical in size etc. using the exact screws on both ends.

5- Look into stepped pulleys! That is a great idea. That way I can keep the voltage where I need it and bring the speed down maintaining torque (I think)

 

I use the fabric backed paper and that little test piece I did took very little to make a whack of sawdust and the finish was nice. I have a piece of Black Hornbeam that I will attempt to make some small billets from. It might make some nice wales on my Winchelsea if this sander works ok