How to open a centering ring wider without a router

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Len B

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I have a stupid situation. I need to open a couple of plywood centering rings by about 2 mm.
I'd like to do it evenly. I would prefer to do it with a jig or some kind of tool but I don't have a router. I would prefer not to hand sand them.
The rings are 7.5 inch with 98mm MMT openings. I am putting two rings together and putting an aluminum retainer through the rings.
That's why I want to open them up.

Does anyone have an idea? I have a drill press and sanding drum but how to jig?

Someone here has done this and is more creative than I am. Help. :wink:

Thanks in advance!
 
Centering rings are cheap, order new ones the right size.
If you value your time at all you will be ahead.

M
 
Yeah. That thought occurred to me. There's no rush on completing the rocket. That's for sure.
Even making them from scratch would likely be faster. There's no way to take off a couple of mm with a fly cutter. That's for sure.

Thanks. (Still curious about other input though)
 
I use a drill press with a sanding drum. First I print out a CR template using OpenRocket with the correct inner and outer diameters and paste it onto the CR to be modded, then sand the interior to match the new ID. Test fit as the ID gets close for a perfect fit. Takes less time than waiting on new CRs, and really doesnt take long at all. A oscillating spindle sander will work as well depending on ID size.
 
Might be able to use a scroll saw or dremel with sanding drum. Darken the amount you want to remove with a pencil, then cut sand until the dark is gone.
 
Might be able to use a scroll saw or dremel with sanding drum. Darken the amount you want to remove with a pencil, then cut sand until the dark is gone.

I mark and use a dremel. A few mm isn't much.
 
I use a cordless Dremel with a coarse sanding drum to final size the center hole of all my centering rings. As long as you keep the Dremel moving in a circle and don't stop it so it "digs in" in one spot, they turn out fine. Like Dick said, 2mm isn't much. I've taken much more material out of the center hole than 2mm before. I've never had a crooked centering ring. I don't measure or mark, I just sand until they fit.

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I use a drill press with a sanding drum. First I print out a CR template using OpenRocket with the correct inner and outer diameters and paste it onto the CR to be modded, then sand the interior to match the new ID. Test fit as the ID gets close for a perfect fit. Takes less time than waiting on new CRs, and really doesnt take long at all. A oscillating spindle sander will work as well depending on ID size.
I’ve done the same thing with very good results. (Although I use Illustrator to create the template.) I use spray cement to tack down the guide.


Tony
 
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I'm going to take a shot at it. Good advice here. Thank you all for the ideas. If I bollocks it up, I'll order new ones. These ones are here, now and should be workable.
 
I see you're up in B.C. so you may have to find another source. I had a similar problem, and this crops up from time-to-time. My solution is to use a paper mache cone sold as a "Christmas Tree" at Hobby Lobby. I roll a sheet of coarse sandpaper around the cone. I put the CR over the cone and, while pressing down, spin the CR on the cone. Go slow so as to not over enlarge the hole; flip the CR over to keep the hole equal on both sides. Works for paper, wood, and other centering rings.
 
Very good idea! We have Michael's here. That's what I am looking for, some way to make sure it's even. I was hoping to do it on the weekend but I had little time.
 
Set a block with the correct distance from outside of the ring at 6 o'clock, to the outside of the drum sander at 12 o'clock. Pull the centering ring towards you and the block at 6 o'clock, as you rotate the centering ring. In my mind this will increase the inner ring diameter the exact amount that you set the block to and be uniform around the entire ring.
 
Very good idea! We have Michael's here. That's what I am looking for, some way to make sure it's even. I was hoping to do it on the weekend but I had little time.

Make a template from heavy cardstock. Use that to mark undersized ring. Sand out to mark (coarse sandpaper to get close, fine sandpaper to hit line exactly).
 
Set a block with the correct distance from outside of the ring at 6 o'clock, to the outside of the drum sander at 12 o'clock. Pull the centering ring towards you and the block at 6 o'clock, as you rotate the centering ring. In my mind this will increase the inner ring diameter the exact amount that you set the block to and be uniform around the entire ring.

This is the kind of jig idea I originally had in mind. I just couldn't quite visualize it. I'm more of a fixer than an engineer.
The main thing idea is to have a stop of some kind and no easy way for the thing to tear it out of my hands when turning it.
 
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