Best way to spin a cylinder without wobble?

julianf · Feb 14, 2021

I'm coming back to something that I've mentioned before here, a type of sander for wood.

Im trying to work out the best way to make the spinning drum bit.

Here is a screen shot from a youtube vid to explain -

What do you think my best way to make this specific part is (mine will be more involved than the above, and made of metal, as i dont like making machines out of wood)

Basically, i want a drum to spin on pillow blocks, and ill have a pulley with a belt to a proper motor.

I figured the drum would be a bit of 4" steel tube, that id weld caps onto the end of, and, i guess, either weld stubs onto the caps, or run a bar down the whole length.

But if its spinning, im never going to get perfect alignment, and it will wobble all over the show.

Maybe i could get it close and then find somewhere with a big enough lathe to just skim the outside of the tube and the end (and then the other end) but is there a way i can do it in house?

I guess i could set it all up, and then somehow mount a grinder of some sort on a carridge, and grind it whilst its spinning, but it may be easier, and with a better result, to find someone with a big lathe?

I really dont want a wooden drum, as it will go out of shape in time.

Its got to be fairly budget, else i may as well buy a pre-built (about £500, but no build time)

Thank you.

julianf · Feb 14, 2021

. said:
I would use a thickwalled pipe, you can centre it in a lathe and skim the outer to get it round.

Yeah, i think that is probably my option. My lathe is not large enough, nor is it close, so i guess ill outsource. If i use a solid bar through the center, then ill be fairly certain of the two ends being in alignment, and then its just a case of getting the "tube" on as best as possible, and skimming the outside.

I cant remember what speed these things run at. I guess, if balance is an issue, ill have to figure out some way of checking the balance and then balancing it up with blobs of weld or something. No idea how id do that, but its not massive rpm anyway.

Agroshield · Feb 14, 2021

julianf said:
But if its spinning, I'm never going to get perfect alignment, and it will wobble all over the show.

If the sandpaper was stuck to the wood passing under a bare metal drum, it would soon put some roundness and concentricity into it.

If it is really bad, mount angry grinder on something you can traverse left and right along spinning drum and control depth of cut off left edge of base board.

daleyd · Feb 14, 2021

. said:
If you use solid bar you run the risk of shearing it as the shearing begins in the middle, by using tube you have no middle to begin shearing.

8ob · Feb 14, 2021

I would keep welding to a minimum, spin up a continuous shaft and bosses for each end , tack weld the bosses to the drum and grub screw to the shaft.

mike os · Feb 14, 2021

Tube probably won’t be round enough anyway

Take your tube, weld on ends then bore out and fit spindle, machine outside using the spindle

Mr Fro · Feb 14, 2021

Personally, I'd make the end bungs an interference fit or use loctite 638. I don't think there's a huge need to weld it up.

Afterwards skim the OD and job done.

Ed. · Feb 14, 2021

A couple of years ago I made a drum sander and also started out with a length of 150mm x10mm steel tube and tried to clean up the outside, I obviously didn't do it right and got awful chatter, it was deafening as the sound bounced around inside the tube. In the end I scrapped that idea and cut out a stack of disks out of 16mm plywoood with a center hole, through the center hole I fitted a machined down steel axle (35mm? final size), all the disks were covered in PVA glue, I welded a flange at one end, and the other flange was tacked to the axle once all the glued disks were placed over the shaft, added the other flange, squashed the wet discs down, the excess glue filled up any space between the axle and the shaft. Once dried, a couple of tacks on the remaining flange and put a couple of bolts into the wood from each flange to help the ply from spinning.

Once that was complete and dried, put it into the lathe and just ran a cutting tool down the length to make a perfect concentric cylinder, gave the ply several coats of PVA/polyurethane to seal the plywood. Last light cut I did made the surface grabby and the velco backed 5" sanding paper sticks to it really well. Put a screw with a washer at each end of the sanding belt to hold it down. The larger the drum, the less dips and hollows you will get if you don't feed the timber in smoothly. I had an accident with it and one of the cutting boards I was sanding, grabbed and flew back at me and hit me on the leg, left a massive bruise as I was on blood thinners at the time. I was spinning that drum at 1830RPM. I ended putting a big sanding belt under it out of 100 grit paper powered by a 12V windscreen wiper motor plus a large cog to reduce the RPM speed and give extra torque. Be aware that as you sand the timber it will heat up and either bend or expand and cause more pressure which will in turn will make it push up more against the drum, which spirals out of control and will grab and eject towards you at a massive speed, so be careful.

Here is a link to the thread in case it may give you some ideas although I did have a metal lathe to do the shaft etc. Not sure if you have one to access and do the machining but there are ways around it, I built this as an attachment to my large wood lathe, nearly all of the metal came from my scrap metal pile I had at the time as you can tell by the rusty axle before I cleaned it up.

Made a drum sander attachment for wood lathe (Pic heavy)

I made a large wood lathe several years ago and had always wanted to build a drum sander, but due to very limited space left in the shed, I decided that my best option would be to make one as an attachment to the lathe rather than having another separate piece of machinery that would take up...

www.mig-welding.co.uk

The motorized belt on the table made a huge difference in the sanding quality plus the added safety, the video at the end will show it working.

Ton-up · Feb 14, 2021

To true up rollers on belt sanders, that have a roller like this, normally made of rubber, is to glue a sheet of sandpaper to a flat board and put it through the machine. You may be able to do this with your metal roller but it may take some time!

Matchless · Feb 14, 2021

Ed. said:
A couple of years ago I made a drum sander and also started out with a length of 150mm x10mm steel tube and tried to clean up the outside, I obviously didn't do it right and got awful chatter, it was deafening as the sound bounced around inside the tube. In the end I scrapped that idea and cut out a stack of disks out of 16mm plywoood with a center hole, through the center hole I fitted a machined down steel axle (35mm? final size), all the disks were covered in PVA glue, I welded a flange at one end, and the other flange was tacked to the axle once all the glued disks were placed over the shaft, added the other flange, squashed the wet discs down, the excess glue filled up any space between the axle and the shaft. Once dried, a couple of tacks on the remaining flange and put a couple of bolts into the wood from each flange to help the ply from spinning.

Once that was complete and dried, put it into the lathe and just ran a cutting tool down the length to make a perfect concentric cylinder, gave the ply several coats of PVA/polyurethane to seal the plywood. Last light cut I did made the surface grabby and the velco backed 5" sanding paper sticks to it really well. Put a screw with a washer at each end of the sanding belt to hold it down. The larger the drum, the less dips and hollows you will get if you don't feed the timber in smoothly. I had an accident with it and one of the cutting boards I was sanding, grabbed and flew back at me and hit me on the leg, left a massive bruise as I was on blood thinners at the time. I was spinning that drum at 1600RPM. I ended putting a big sanding belt under it out of 100 grit paper powered by a 12V windscreen wiper motor plus a large cog to reduce the RPM speed and give extra torque. Be aware that as you sand the timber it will heat up and either bend or expand and cause more pressure which will in turn will make it push up more against the drum, which spirals out of control and will grab and eject towards you at a massive speed, so be careful.

Here is a link to the thread in case it may give you some ideas although I did have a metal lathe to do the shaft etc. Not sure if you have one to access and do the machining but there are ways around it, I built this as an attachment to my large wood lathe, nearly all of the metal came from my scrap metal pile I had at the time as you can tell by the rusty axle before I cleaned it up.

Made a drum sander attachment for wood lathe (Pic heavy)

I made a large wood lathe several years ago and had always wanted to build a drum sander, but due to very limited space left in the shed, I decided that my best option would be to make one as an attachment to the lathe rather than having another separate piece of machinery that would take up...

www.mig-welding.co.uk

The motorized belt on the table made a huge difference in the sanding quality plus the added safety, the video at the end will show it working.

and will grab and eject towards you at a massive speed,

How do you know that? :doh:

Ed. · Feb 14, 2021

Because the massive bruise I got educated me, but not before I did it again! I thought that if I was very careful I could avoid that risk so I was being extra careful and it still did it again. So that is when I decided I needed to do something about it, there wasn't going to be a third time! I didn't end up using that heavy knurled roller as I found that the table belt on its own prevented the timber from flying back.

Screwdriver · Feb 14, 2021

A steel tube is a bit more tricky but if you're making the entire thing out of steel with pillow blocks, what you are making is a basic lathe anyway. Just build it as accurately as you can and then jury rig a cutter/grinder to machine the tube to round in situ using your proposed belt driven system.

slim_boy_fat · Feb 14, 2021

How wide is this going to be?

Kram · Feb 14, 2021

How long? half, meter?
Turn a shoulder on end peices so they are perfectly aligned then shrink fit them.
4" solid aluminium bar is not that expensive. For a short lathe you could make in several lengths turn then shrink fit together.

Planer/thicknessers are similar? Except they have spinning blades instead of a drum?

Screwdriver · Feb 14, 2021

Also very much depends on the precision of your 4" steel tube. Many types will only be approximately round to a wide tolerance plus the inside bore might not be perfectly concentric and unless it's an extrusion, also have a weld seam to contend with.

Do you already have a length of tube you're considering using?