Yesterday I uploaded a Photo Album of the sanding arbors I was making. Today due to the popularity of that I am posting a detailed step by step article of the same project. I'll add the holder I made for it as a special bonus feature at the end too.
Step 1: Tools and Materials
These are the tools I used. If I had a metal lathe I would have used it instead.
Milling machine used as a drill press
Letter Q twist drill
3/8" X 24 TPI tap
5/8" combination wrench for arbor bolt
3/4" & 7/8" wrenches for T slot hardware
Plunging Wood Router
1/4" spiral up cut router bit
#24 twist drill
3/8" twist drill
9/16" paddle bit
1/4" end mill
6 inch calipers
Transfer Punch (see text)
Hole saw (see text)
a piece of Melamine, or MDF large enough to cut (4) 6" diameter circles out of
a small scrap of hardboard (to make the router trammel out of)
an 8D nail for the trammel pin
1/2" OD heavy wall pipe (the pieces I used are about 10" long)
3/8" X 24 TPI bolts about an inch long
2 washers that fit snugly on 3/8" bolts for each arbor made
6" PSA sanding discs assorted grits
80 grit sanding belt
That is about all I can think of now.
Step 2: Make the Router Trammel
Everyone's wood router is going to be different. Make a trammel out of some hardboard, or other sheet material that fits yours. I'm just going to offer some brief tips here for how I make mine. I take the base plate off my router and use a transfer punch to mark the holes I need to drill for screws. I drill those out, then countersink them for the screw heads. I mount my trammel plate I'm making to my router and plunge the bit I am going to cut with through the plate. Now I take my trammel plate off the router and figure out where I need to put my pin.
Using a square I draw a straight line through the diameter of the routed hole then with a compass set for the size circle I want to cut I figure out where the center of the trammel pin goes by drawing an arc to the routed hole in the trammel plate with the compass point on my center line. I grind the head of an 8D nail down until it is 1/4" round with a bench grinder, then I cut the nail so it is about a half an inch long with a hack saw. I chamfer clean the cut up on the bench grinder. I drill and counterbore my trammel plate in the marked spot for the nail and insert it. Then I enlarge the bit hole with a hole saw so chips can eject. Screw the finished trammel plate to my router and use it to cut circles with.
That's the brief version. I hope everyone gets the idea. Oh yeah, you probably want to use a plunge router for this operation.
Step 3: Cut Sanding Discs
Now it is time to put your router trammel to work cutting your sanding discs out with it. I laid mine out with the same cheap compass I used to make my trammel with. I wanted to make sure I had meat where I was going to cut. Drill for your trammel point with the #24 drill bit. Set the trammel point into your center hole and start routing. I cut away maybe a quarter of an inch deep or so a pass. When I'm done with a pass I go counterclockwise backwards to clear the cut, and unwind my power cord. On the last pass when I break through I skip a little to hold the circle up. I leave about a half of an inch or so in the beginning, then halfway around I leave another half of an inch skip. Then when I get back to my first skip I cut it away and turn the router off. If you don't leave those skips in your cut, well just use them because you don't want the running router to fall down.
I'm going to take a bogus after the fact picture of my sheet with holes cut out of it. I'll throw my cheap compass on it so you can have a look at it too. Take note how the sheet is blocked up over my workbench with some foam on the side I cut on. I don't want big circles cut into my workbench. I bet you don't either.
Step 4: Make Mandrils
I thought about calling this step tap pipes because that is all it really is but that just doesn't sound right to me. Anyhow let's get to it.
If you have a metal lathe then lucky you, use it. Me, all I got is an RF-32 mill/drill so I'm going to use that. I'm sure if someone is really determined they could just use a drill press to do this. Other than drilling the only feature that I used of my mill is the t slots for holding the vise. Drill presses have slots for mounting things to them too.
At first I didn't want to get this involved with the project. I mean why make things harder than they have to be? I ended up snapping my letter Q bit trying to run it with a hand drill into a piece of this tubing, then when I tapped the pipe I didn't get the threads concentric with it at all.
OK so now time for round two. I ground my letter Q bit back into shape and pulled my vise off my workbench, and put it onto my mill table. This is how to get a prefect tap into pipe. Chuck the pipe into the chuck on the mill. Then position the vise so it holds the pipe. Tighten the vise jaws down where it is holding the pipe. Then tighten the vise base itself down. I should add have the head of the mill loose while aligning things too. Then once the vise is aligned and the pipe held in it tighten that down as well. Now release the pipe from the chuck and chuck the drill bit to size the inside of the pipe for tapping. Drill the pipe. Remove the twist drill and put the tap into the chuck. Start the tap into the pipe. Release the tap from the drill chuck. Now take the pipe out of the vise and put it into another vise and finish tapping it.
It worked for me here.
Step 5: Wrapping Things Up
It should go without saying that you are going to have to drill your disc center holes up to clear your bolts. I used a 3/8" twist drill for a reasonably tight fit on my 3/8" x 24 TPI bolts I used. I step drilled the holes up with some random intermediate twist drill bit to maintain concentricity with my trammel pilot holes. I dug through my junk washer collection and found washers that were a good fit on my bolts and put a washer on either side of my discs.
I used 6" PSA sanding discs on my wooden discs I cut out. Here's where the craft knife and hat pin come in. With the PSA disc stuck to the wood disc I flipped that over sandpaper side down, and put it up on some scrap blocks. Then I carefully perforated the center hole with the hat pin all the way around the hole. I flipped the disc back over and carefully cut the hole out with a craft knife following the perforations I'd made.
Previously I'd also chamfered the bolt holes in the discs a little bit too with a countersink. The goal here is for these wooden discs to run reasonably true.
Oh, I almost forgot a step. Before you go mounting the PSA discs to the wooden ones take the discs for a spin on your machine and sand the edges with a broken sanding belt. I used a broken 3"x21" 80 grit belt I have kicking around. It really adds to it. I broke the sharp edges on my disc with sandpaper too. Have fun. I ran at 695 RPM according to the speed chart on my mill. It seemed good to me.
Step 6: Make a Holder
This is an added bonus compared to my photo post of yesterday. I liked this project a lot. I liked it so much I made 4 of these things. Mainly because I didn't want to fool with sandpaper while I was working on stuff. I always want to step through grits, well you get the idea. Anyhow having 4 of these things makes for a storage issue. Initially I was going to make one mandrel and a few discs to go with it. With that plan I had an idea for a partitioned box to keep all of the discs in. All of that is out the window now with 4 discs and mandrels to store.
Then I thought of another box I could make, and I arranged the discs on a workbench and looked at it. I rearranged them and hit upon a nested arrangement that I fancied. I did a few calculations and long story short here's how to make this holder.
Get a scrap piece of 2x4 at least 16" long. Mark the center of the thinner side lengthwise down. 3 inches up from one end mark to drill. 3 and a half inches from that mark to drill again. Keep marking at 3 and a half inch intervals until you've enough holes for all of your disc shafts to fit in. Center punch those marks and drill them through with a 9/16" paddle bit. I used a drill press vise myself for this operation.
If you do a good job your holder will roll around nicely too. I know mine does.
Step 7: Acknowledgements
Again I have to give a shout out to Dave Bardin over at G+ in the Hand Tools community. If it wasn't for me watching his video and getting tool envy seeing his slow speed sander I wouldn't have come up with the idea to make these sanding discs. His machine is still cooler but these discs kind of do the same job too I suppose.
Here's a link to the video