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Author:  old man [ Wed Nov 02, 2005 10:36 am ]
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I'm making my bridge today and had trouble cutting the slot.   Im using a 3/32" downcut bit in ebony. I was trying to take about 1/16" depth at a time. First cut was fine, 2nd cut it jerked a couple of times and screwed things up. I then switched to a 1/8" bit to clean it up and thought I could use a thicker saddle. Same result. I'm using a jig to guide by, and the bridge is mounted solid. Am I just trying to take too big a bite at one time? Talk to me, please.

BTW, I filled the slot with epoxy mixed with ebony dust to try and salvage it tomorrow. Any suggestions?

Ron
Author:  RussellR [ Wed Nov 02, 2005 10:40 am ]
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What are you cutting with Ron, Laminate Trimmer, Router, Dremel ?

Author:  old man [ Wed Nov 02, 2005 10:54 am ]
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Its the new dremel 450, I think that's the number. It doesn't bog down at all, so I think the power is enough. The bit is brand new, so it's sharp enough. I have a laminate trimmer and a large router, but I don't have a collet that will fit the bit I have.

Ron
Author:  RussellR [ Wed Nov 02, 2005 10:58 am ]
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I think It is the shank chattering, in ebony I would halve your cut, and make more passes and have as little shank out of the chuck as possible.

I have switched to using my laminate with a 1/4" shank bit, it avoids the chatter.


Hope this helps Ron
Author:  old man [ Wed Nov 02, 2005 2:27 pm ]
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Thanks, Russell
I think you're right. The Dremel has enough power but not enough mass. I found the bits I need and will order them tomorrow with 1/4" shank, then I can use the laminate trimmer or my plunge router if needed. I had a really neat jig made for the job, though, that was a custom fit for the Dremel. Oh, well, I'm learning a lot from this first guitar.

Ron
Author:  Steve Kinnaird [ Wed Nov 02, 2005 2:46 pm ]
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Ron, I've had the same problem. And I think you are right about the mass. I thought that the Dremel was too light for the type bit you and I have been using. A spiral "grinder" type bit--not sure what to call it, but it came in my Dremel kit--works much better. However, the lam trimmer should solve your problems.

Steve
Author:  old man [ Wed Nov 02, 2005 3:23 pm ]
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Thanks, Steve
Seems like no matter what kind of problem one has, someone on the forum has experience with it.

Ron
Author:  CarltonM [ Wed Nov 02, 2005 3:29 pm ]
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There are adaptors that allow you to use 1/8th" shanks in 1/4" trimmers/routers. I got one from Lee Valley. I haven't used it yet, though, so I don't know if it's a disaster waiting to happen....
Author:  Shane Neifer [ Wed Nov 02, 2005 4:19 pm ]
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Ron,

Just another suggestion, try jigging up so that there is no way that your dremel tool can go beyond the area you want to carve out. What I mean is build a jig that confines the travel of you dremel base to the area of the mortice. And take light passes. Your carbide downcut spirals at 1/16 inch passes at over 20,000 rpm should be fine....

IMHO

Shane
Author:  Frank Ford [ Wed Nov 02, 2005 4:43 pm ]
Post subject: 
That's right, the Dremel has really crummy bearings and such poor rigidity
that the entire body of the tool flexes under load, so you have to take very
light cuts to avoid those problems.
Author:  BlueSpirit [ Wed Nov 02, 2005 5:34 pm ]
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Ron,
I used to use a Dremel, and had basically the same problem. I stole an idea from John Mayes (His dvd's again) and bought one of those vices that moves forward, sideways, and can rotate in place. I chuck my bit into the drill press, put my bridge into the mounted vice, angle it properly, turn the drill press on and crank the handle that moves the bridge from side to side. I take little bits at a time, and as long as everything is tight, nothing moves. The trick is to get the angle right before you start, and use a 1/4" to 1/2" shank. Hopes this makes sense.
The vice is called a "Cross-Slide 360 Vise/Drill Press/Milling Machine 3axis" and I paid $34.95 on e-bay.
Author:  RussellR [ Wed Nov 02, 2005 8:01 pm ]
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Your more than welcome Ron

You probably know this already as I know you are a very experienced woodworker, but make sure whatever jig you use for the small diameter 1/4" bits are held firmly as they are very easy to break, and expensive.

Thats the thing with Jigs, Fixtures, Etc, it is a matter of finding what suits you, I think I'll still be changing things around in 30 Years Time, if I'm lucky enough to be alive and still doing this.
Author:  John How [ Thu Nov 03, 2005 12:52 am ]
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I use a PC laminate trimmer in the jig shown in our jigs section. the jig holds the router so that it cannot move side to side. I use a 1/4" shank bit with 1/8" cut and I cut the whole depth in one pass. Never a chip or problem.
Author:  old man [ Thu Nov 03, 2005 1:01 am ]
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Thanks everyone. John, that's the jig I made and it is really nice. But I made it to fit the Dremel. I'll redo it for the laminate trimmer.

Ron
Author:  Steve Kinnaird [ Thu Nov 03, 2005 4:21 am ]
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JH--(John How)--first time I've seen that jig. I like it mucho!
Well done.

SteveSteve Kinnaird38659.5161226852
Author:  old man [ Thu Nov 03, 2005 5:34 am ]
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I shaped three ebony bridges yesterday using John's other jig and they came out perfectly. Good stuff.

Ron
Author:  John How [ Thu Nov 03, 2005 5:37 am ]
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I stopped using the shaping jig and started doing them freehand on my spindle sander. That way they all look the same only different
Author:  old man [ Thu Nov 03, 2005 5:40 am ]
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John, do you have a special way to shape the taper from bass to treble on your bridges, or do you just eyeball it?

Ronold man38659.5760532407
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