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Home made thickness sander issues

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Home made thickness sander issues

Postby Stuart Mansell » Fri Aug 11, 2017 7:36 am

Hello everyone, this is my first post.
I'm a novice guitar builder with only one under my belt, built on the eigm course run by Stephen Hill in Spain. I'm v slowly building No.2 but spend most of my time in the shop making jigs and tools and what have you.

My current project is a home made thickness sander.
I found loads of designs and pictures online but one spoke to me so I've been recreating that one.
The maker thanks the MIMF on his site which is how I found this place.

Here goes....This is the problem.

I have cut 25ish 18mm ply wood discs which will be stuck together onto a 12mm steel shaft to create the drum.
So each disc needs to have a 12mm hole cut in the middle so it can fit onto the shaft.
I don't have a pillar drill so I created a jig and used a 12mm router bit.

I ran a couple of tests last night. I routed out 2 of the discs and put them onto the steel shaft however they fit a little too loosely. It seems there is about 0.1mm/0.2mm discrepancy between hole and shaft.

Before doing this is asked the chap who made it, how his wooden drum was fixed to the steel shaft. He said all the discs were glued to each other on the shaft and its fixed in place by that alone. (I'm reluctant to keep asking him more questions.he's been very kind already.)

I imagine for his method to be effective, one would have to have a pretty tight fit in the first place...something I don't have.

So either the shaft is a little thin or the router bit is cutting wide. Annoying. Both were bought with 12mm being the spec.

The options I have come up with so far are...

1. Try and match the holes i cut to the shaft by buying an 11.8/11.9mm drill bit (don't think router bits come in that size) and drilling the holes out. (I don't have a pillar drill so Id also have to make some kind of jig to make sure all holes are consistent.

2. Try and make the shaft match the hole. Ie adding some kind of layer of something. Tape? Glue? Etc although this seems to just be another element that could cause the drum to slip.

3. Go with what I have and hope the glue fills the tiny gap and holds it all in place.
Is that something tight bond does?

4. Find a method of securing the drum to the steel shaft at either end.

If anyone has any insight or ideas on any of this I love to hear them. I'm very eager to avoid any major issues down the line.

Thanks for reading

Stu
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Re: Home made thickness sander issues

Postby Charlie Schultz » Fri Aug 11, 2017 9:35 am

Hi Stu, welcome.

One thought might be to add some tape to fill up the gap, but then make two more smaller diameter discs with the proper diameter hole. Glue/screw one of those discs onto each end of the drum, then pin that to the shaft by drilling a hole through the smaller diameter disk into the shaft and inserting a pin. You'd have to make sure the pin is sized to handle the torque at start up.
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Re: Home made thickness sander issues

Postby Craig Bumgarner » Fri Aug 11, 2017 10:12 am

I used a shaft with keyway the full length of the shaft (McMaster Carr) and made a hardwood key that fit the shaft. I cut keyways in each disc and slid them on the shaft. You might consider replacing the shaft with one that is keyed and doing it that way. Otherwise, I think glue around the shaft and in the holes will do it, you have a lot of surface area there.
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Re: Home made thickness sander issues

Postby Stuart Mansell » Fri Aug 11, 2017 10:19 am

Thanks chaps. Couple of good ideas.
Don't know why I didn't think of that Charlie. Seems fairly straight forward.

I like your idea Craig but feel that might be more of a complete rethink and hence a lot more work.

I think perhaps I'll go with some tape then glue it all and if there's issues I could implement your idea charlie.

So will the tite bond be enough to fix it to the shaft? Or should I be looking at something specific for wood/metal bond?
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Re: Home made thickness sander issues

Postby Bob Gramann » Fri Aug 11, 2017 10:23 am

Do you have a machine shop nearby? They can drill your precise holes (for a fee, of course). When I built a drum sander a couple of decades ago (I replaced it long ago with a Delta), I had the machine shop make me a stepped shaft with threads at each end of the drum section. Nuts and lock nuts (and monsterr washers) on each end were sufficient to hold the drum (made of disks glued together) tight. I would expect that any gaps between the disks and the shaft would allow flex in the drum and severely limit accuracy. The machine shop also made a keyed slot in the end of the shaft for me to lock the pulley.

When I had the whole thing together, I was able to true the drum by sanding it against a very flat board with sandpaper glued to it.

I finally abandoned my homebuilt and bought a factory made machine when I couldn't get the precision I wanted with my manual feed device. I wanted a feed belt. I figured the amount of use that I gave the machine made it worth the cost. My figuring was correct.
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Re: Home made thickness sander issues

Postby Barry Daniels » Fri Aug 11, 2017 10:25 am

Trying to drill holes with a router bit is your problem. Get a drill bit and a drill press. You will end up getting a drill press eventually anyways. It is the first stationary tool that most guitar builders purchase.

I recommend that you keep trying until you get a good tight fit. Filling with tape or anything (except for structural epoxy) will be asking for problems down the line. If you go the structural epoxy route you will need to thicken it with fiber reinforcement so that it will be thick enough not to run out. But I would still worry about the shaft coming loose from the glue and turning inside of the discs. Definitely don't use Titebond! It won't stick to metal.

Craig's keyed shaft is the best way to do this job.

I am also concerned about the size of your shaft. When you put that much weight on a shaft and spin it fast it may flex. I wouldn't go any smaller than 20 mm.
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Re: Home made thickness sander issues

Postby Bryan Bear » Fri Aug 11, 2017 10:31 am

My drum is 25.5' long made up of 34 MDF disks. I glued them all to the shaft with polyurethane (PU) glue. I don't remember how much slop there was between the hole and shaft but I don't think it was a super precise fit. It wasn't really bad either. I held the shaft vertically an glued each disk to the previous and the shaft all at once, then weighted the whole thing down to clamp. PU glue foams and expands while it cures if there are any gaps. This does not mean that it is "gap filling" at least not in any structural way. But with all the disks glued together as a solid unit I was left with a tremendous amount of surface area around the shaft for gluing. The whole thing is now rock solid and has shown no signs of coming apart.

You have about 70% the linear gluing surface area; actual surface area will depend on your shaft I can't remember if mine is 3/4" or 1" but certainly bigger than yours. My gut tells me you will be okay but I don't really know how much oversized your holes are. . . Definitely don't use wood glue. Epoxy would probably be the best option. I would guess that if it isn't going to hold, you will find out while you are first spinning the drum and truing it. That will be way more aggressive than any sanding you should be doing in use.
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Re: Home made thickness sander issues

Postby Alain Lambert » Fri Aug 11, 2017 8:43 pm

I don't think a shaft 12 mm or 1/2in is strong enough. Use 3/4 in or 19-20 mm. If your shaft flex during sanding, you will not get equal thickness on your board.
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Re: Home made thickness sander issues

Postby Bob Francis » Fri Aug 11, 2017 9:56 pm

Alain Lambert wrote:I don't think a shaft 12 mm or 1/2in is strong enough. Use 3/4 in or 19-20 mm. If your shaft flex during sanding, you will not get equal thickness on your board.

I agree with Alain. I had a narrow (+- 12 inch) sander and made the mistake of using 1/2"m rather than 3/4". It was okay but not accurate or repeatable due to bouncing as described.
As to the ply pieces a friend built a similar setup (with 23/4 shaft) and was surprised at how irregular his plywood disks were despite having taken great care in cutting them out.
That's a simple problem to resolve with 80 grit paper on the table and slowly engaging the drum onto it.
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Re: Home made thickness sander issues

Postby Stuart Mansell » Sat Aug 12, 2017 6:52 am

Yes I intend to true the plywood drum with some course grit paper before I use it.
Intetesting remarks about the shaft diameter. The plans im copying used a 1/2" shaft.

I will proceed as planned but be prepared to switch out that shaft for thicker one should there be issues. Thanks for the heads up.

Barry, regarding the router. Why is it an issue to make the holes this way?
12mm router bit/12mm drill bit. Should give me a 12mm hole no?

I'm no expert tho so don't know.
Thanks

Edit: I've been searching for keyed shafts as I didn't really know they were an option.
It seems they must be called something different in the UK. The term 'keyed shaft' only throws up results from US stores/website.
I also found out recently that its almost impossible to get adhesive backed rolls of sandpaper over here. Annoying
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Re: Home made thickness sander issues

Postby Bryan Bear » Sat Aug 12, 2017 10:33 am

I don't use adhesive backed sandpaper. My method is stupid simple! I use regular rolls of inexpensive paper. I cut a diagonal on the end equal in length to the circumference of my drum. That becomes the edge on the right hand side of the drum. I use duck tape strips too secure it around the edge of the drum then just wrap the paper tightly as I turn the drum by hand. I end up with a spiral of paper covering the whole drum. I cut off the end and tape it down like the other side. Sometimes (but not always) the paper will stretch a little bit or I didn't get it wrapped tightly enough (Not sure which) but the paper will loosen a bit after a few mins. of sanding. I just stop, pull it tight again and retaps the left side; problem solved.

This probably wouldn't be an issue with nicer paper but I like being able to pick up a roll from down the street and not feeling bad if I let it get gummed up.
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Re: Home made thickness sander issues

Postby Barry Daniels » Sat Aug 12, 2017 10:39 am

Routers are not designed for drilling holes. It is that simple. They are designed to cut sideways so when you try to cut vertically, the bit can easily move sideways throwing your hole out of alignment making an oversized hole. Drill bits have no side cutting capability so the vertical cut is self aligning. But a drill press is necessary to keep the hole truly vertical and aligned.

Regarding alternate search terms for Keyed Shaft, you might try "slotted shaft". But really any machine shop or machine supplier will be familiar with this type of shaft. Another possibility is a place that makes go-karts. They use keyed shafts.

One thing to consider about having a shaft with a key slot is that it actually weakens the shaft so you would need a larger diameter shaft to make up for the missing metal.
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Re: Home made thickness sander issues

Postby Stuart Mansell » Sat Aug 12, 2017 4:26 pm

Yes barry thanks . this, I think, is what has happened now we're discussing it.

After setting my jig for the centre of the first disc, I routed out a mill deep as a test and it was off. I could tell why Street I wad so careful when setting the jug so it wad perfect centre. I traced the movement to the plunge attachment. The main body of the router was rocking ever so slightly on the two sprung legs.

I think drilling the rest is the way to go.
Thanks for that

Yes brian I've actually seen a few folk who do a similar paper attachment method to you. I'll probably go for something similar. Cheers
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Re: Home made thickness sander issues

Postby Stuart Mansell » Sun Aug 13, 2017 4:37 am

Sentence should've read.
"I couldn't tell why as I was so careful when setting the jug. It was perfect centre. "
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