grit edged rod saw

[darryl]

Little blobs of plastic stick to the wire, then have to burn off, or be scraped off by the advance of the hot wire through the foam. Not a very nice result, really. Styrofoam is the same, just less so, and normally acceptable.

[Beazld]

I find for hot wire cutting styrofoam that if the wire gets gummed up I turn the power on and use a piece of scotch bright or steel wool while the wire is hot and it cleans up fine.

[garyhlucas]

You might try a surface set diamond core drill. Would cut real smooth and they run true. Not sure if they still make surface set, might be only matrix type now.

[darryl]

Today I found a piece of cold rolled rod that is straight- that's a bonus. I built an mdf box around it and built it up to 3 x 3 inches square. Once the glue is well and truly dried I'll set it up on the table saw to carve it round and 2-3/4 diameter, then spiral wrap and glue the sandpaper to it. I bought a zirconia belt to hack for this use, and I'll have to devise a way of wrapping the belt such that it doesn't overlap itself. That's easy without glue-. I'll have to put the full wrap on the drum, then wrap some rope or something around about half of the length to hold that in place. Then I'll unwrap the loose end and apply the spray glue and wrap that tightly together, then repeat for the other end.

OR- I can wrap the sandpaper around the drum to find the helix angle, then set the belt on the workbench at that angle and lay the drum onto it. If I get the angles exactly right, I'll be able to hand-form the sandpaper around the drum perfectly. This is 6 inch wide sandpaper around a 2-3/4 diameter drum, so it looks like about three turns over the 24 inch length of the drum. I'm expecting the thickness of the glue to change the wrap angle slightly, so I'll be very careful about the setup.

Being the impatient type, I'm going to first work this drum across the foam test piece by hand to see how quickly I can reach the correct depth for this carving. The steel rod will be the guide bar, riding in guide slots. Once I motorize it, I could still 'saw' it back and forth while the motor spins the drum.

[djc]

I am late to this, but would these people have something that would suit?

https://mitchellsabrasives.com/

[darryl]

I haven't heard of abrasive cord before, but I'm not surprised. Won't help me in this case, but interesting nonetheless.

Today I set up a jig on the table saw and now I have in my hands a drum, or a mandrel if you call it that, to fasten the sandpaper to. I mounted the rod up on blocks, positioned directly above a set of dado blades, and clamped things in place. I rotated the glued-up assembly on the rod and turned that by hand while sliding it back and forth to 'mill' the entire length of the mandrel. Actually came out really nice, taking me about a half hour to set up the jig, and another half hour to do the machining. After my lunch I'll wrap the paper onto it to see how it's going to fit.

[reggie_obe]

The final end product of this endevour is what?

[darryl]

Ok, looks like it will take about 40 inches of paper to make it from end to end of the drum, so the 48 inch sanding belt I ruined to make this thing was a good choice. And yeah, I've been saying paper, but this is actually a cloth-backed abrasive strip. The critical step is coming up- getting it glued down properly.

[darryl]

The final product is something I can't divulge just yet. When I can I'll post pictures.

[djc]

The critical step is coming up- getting it glued down properly.

If you do not yet have a method in mind, have a look at how wide belt drum sanders do it (maybe the manual for a Jet or Grizzly one would show the process). The paper is wrapped in a spiral around the drum. The beginning and end of the paper are cut at a slant, folded inwards and trapped/clamped into the drum.

[darryl]

I glued the sandpaper to the drum last night. I compensated for the decreased helix angle due to the thickness of the glue, but not enough. I got a bit of overlap, which I was lucky enough to be able to cut away using scissors, but I ended up with one bubble anyway. It's usable, but I'm making another one today.

The most interesting method I've seen is the spring-loaded tensioning device at one end of the drum. Looks like it should work.

The home made spiral wrapped drums seem to use carpet tape to hold just the ends of the sandpaper strip. Any stretching at all of the paper would have it losing contact with the drum. Not really seen a method I like yet. I still want to glue the whole area down. I can throw the whole thing away when the grit loses its bite. I'm not worried about saving the drum. From my experience, sandpaper lasts longer when it's glued down, and not free to wrinkle or fold.

Todays project is using 36 grit, yesterdays used 60 grit. The one I make today will be a bit smaller in diameter, so it will be the roughing one, and the other can smooth the cut with just a couple passes. Stay tune for the home made drum sander saga-

[darryl]

Made another drum today and contact cemented the sandpaper to it, as I did with the last one. The difference today is that I used wider paper (cloth) and a much narrower helix angle- about a quarter turn in 5 ft or so as a guess. What worked is to be able to lay the drum on the sandpaper with one side of the drum near one edge, and the other side of the drum near the other edge of the sandpaper. That's what I'm calling the helix angle. That way the full length of the drum is touched down on the paper at one time. Then it's a matter of pressing down on the drum while rolling it onto the paper in both directions. It was a piece of cake to finish squeezing the paper down by hand and watch the edges come together.

This drum is 2-5/8 diameter, yesterdays drum is 2-3/4 diameter. Yesterdays paper is 6 inches wide, today it's 8-1/4 wide. Yesterday I had to wrap the paper onto the drum, today I rolled the drum onto the paper. It made all the difference. And like I said, having to throw the drum away with the worn out paper is not a big deal. Today I built the drum in half the time it took me yesterday. It takes about a bucks worth of mdf, and it's easy. The worst part is the sawdust from milling it round.

The ways I've seen the drum built on line look to be time-intensive. My method of milling the drum over dado blades on the table saw works great. Still some improvements I can make, but that's beside the point. Soon I'm going downstairs to try this one out.

[darryl]

There is metalworking content in this topic- I will make two flanges to fit the central rod and to fasten to the ends of the drum. To motorize this I'll need to use some kind of coupling between the motor and the drum shaft. I'd like to use the motors front end bearing as the control at one end, and the other end will have its own bearing. I'll need to make some kind of frame to keep the alignment. It would be cool if the motor shaft and the drum sander shaft are the same diameter. That will make the coupling easier, but also require the drum shaft to run very true.

Because the motor will be by far the heaviest part of this, I'll have to arrange a pivot so the weight is supported and the drum shaft can pivot up and down to some extent. I want to wrap something around the motor that has points where it can pivot on. The motor shaft and the drum shaft remain aligned to each other. I know this can be a bit daunting- the extention to the motor shaft would be about two feet in this case. Pretty easy to set up horrible vibrations that can destroy things in seconds-

[darryl]

Ok, the new drum does cut faster than the previous one, but not by that much. The surface left behind is not too bad the way it is. That leaves me with another option, which is to make a third drum, but use a coarse zirconia paper, the same grit as the second drum- which is aluminum oxide. I'll take the longer wear life of the zirconia if I do make this third drum. Plus I can refine the drum design for an even closer fit on the shaft. The second drum will serve as a backup, and the first one will be the polishing drum if I even decide to use it.

Nothing more to bore you guys with on this topic until I get the machine part built.