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strange second ledge using SM binding bit?
http://luthiersforum.com/forum/viewtopic.php?f=10101&t=18707		 Page 1 of 2
Author:  JRE Productions [ Mon Sep 08, 2008 9:20 am ]
Post subject:  strange second ledge using SM binding bit?
Just got the SM binding bit set up for my routing jig. On the inside corner of the rabbet that it cuts there is a small ledge. Its maybe .015x.015 in size. To get my binding to lay flush against the back wall, I had to take a chissels and remove it. I know there should be some clean up, but why is there this ledge? I assumed I would have to clean up a round corner inside, but this is a defined ledge.

My jig is plum and level in both directions. The bit does not look like it should cut a ledge as the carbide tips look square. Any thoughts?

Joe
Author:  TonyKarol [ Mon Sep 08, 2008 9:26 am ]
Post subject:  Re: strange second ledge using SM binding bit?
My guess is that something tipped, or is loose somewhere .. I assume you went around twice at least, as thats how a second cut would have been created. Possibly a chip got under the base and tilted it second time round ???
Author:  JRE Productions [ Mon Sep 08, 2008 9:29 am ]
Post subject:  Re: strange second ledge using SM binding bit?
I'll double check on my test boards, but I am pretty sure the very first pass on the test piece did this too.

Yes I went around twice. I did the climb cuts, then ran the guitar around the opposite direction. Then around again and cleaned up anything missing. The ledge is consistant all the way around.

Thanks,

Joe
Author:  Hesh [ Mon Sep 08, 2008 9:50 am ]
Post subject:  Re: strange second ledge using SM binding bit?
Yeah it sounds like something moved or came loose as Tony suggested. I find that when routing for my rosettes if I don't vacuum the dust away the router base rides higher on the dust and the channel is not uniform in depth.
Author:  LanceK [ Mon Sep 08, 2008 9:59 am ]
Post subject:  Re: strange second ledge using SM binding bit?
I always chamfer the inside corner of the binding strip so that it lays better in the ledge. A quick swipe with the scraper is all it takes.
Author:  JRE Productions [ Mon Sep 08, 2008 10:56 am ]
Post subject:  Re: strange second ledge using SM binding bit?
The practice cuts were done on LP shaped body cut out of pine. (2x8" glued together) As far as I can remember, there was a ledge on all cuts I made with the new setup. That is to say, I took a first pass and pulled it out and looked. There was a ledge. Then I went in the rest of the way and the ledge remained. Its quite small and took about 15 minute for me to clean it out around the entire guitar body, but I don't think it should be there.
Author:  Howard Klepper [ Mon Sep 08, 2008 11:17 am ]
Post subject:  Re: strange second ledge using SM binding bit?
So are the corners of the cutting edges on the bit square?

It's a good idea to knock a bit off the inside corner of the binding piece (scraper, file, sandpaper all work) to ensure a tight fit, but you should not be seeing a .015" ledge in there. Or any extra ledge. I suspect runout in your tool. Is it a dremel or similar?
Author:  JRE Productions [ Mon Sep 08, 2008 11:27 am ]
Post subject:  Re: strange second ledge using SM binding bit?
Howard.

Here is the jig (not quite finished in the pic). The slides are ballbearing and there is no slop left to right or front to back. It moves up and down smooth, though I do think its a tad bit heavy. The donut next to it on the bench was slightly reshaped to clear the top carve of the archtop I am building for #1. The donut was then screwed to the under-side of the jig and with a hole cut large enough to just clear the binding bit. I screwed this jig to my bench top so it wouldn't move. Then I made the standard cradle to hold the archtop body.

Image
Author:  JRE Productions [ Mon Sep 08, 2008 11:29 am ]
Post subject:  Re: strange second ledge using SM binding bit?
Here is sort of whats happening. 250 tall binding slot cut using the .120 wide bearing. The little ledge was about .015 tall and wide.

Image
Author:  Rod True [ Mon Sep 08, 2008 12:22 pm ]
Post subject:  Re: strange second ledge using SM binding bit?
I'd re-check the cutter because if it is uniform along the entire channel then I would think there has to be a nick in the cutter.

So, after ONE pass, this ridge is produced right?

Here's another test to do. Remove the router from the binding jig, take a piece of scrap and cut a long straight channel in one edge with the binding bit and one of the bearings. Is the ridge still there? If so it's the bit. If not it's part of your process.
Author:  Michael Dale Payne [ Mon Sep 08, 2008 12:45 pm ]
Post subject:  Re: strange second ledge using SM binding bit?
I agree with rod here to get that kind of ledge the cutter has to have a nick or step in it that coincides with this second ledge sort of on the order of a molding cutter. The strange thing is that if the ledge is constant and consistent then both or all three flutes would have to have the same error. The only other thing I can think of is a narrow but deep first pass and a full width and shallow second. But I suspect if You inspect the bit you will find a corresponding flaw in the cutters.
Author:  Dave Stewart [ Mon Sep 08, 2008 1:58 pm ]
Post subject:  Re: strange second ledge using SM binding bit?
Put it in a router table & make a pass......if results are indenticle, it's the bit.
Author:  JRE Productions [ Mon Sep 08, 2008 2:00 pm ]
Post subject:  Re: strange second ledge using SM binding bit?
Thanks everyone. I will take a look at it tonight. In the meantime, the archtop has its binding all taped up and installed. Will look at it tonight too!

Joe
Author:  Howard Klepper [ Mon Sep 08, 2008 2:56 pm ]
Post subject:  Re: strange second ledge using SM binding bit?
Thing is, if one flute has a good corner and the others are nicked, you won't get that pattern. One could nick all the flutes, but on what if it has only been used on wood (or has it?)? Possibly one flute was set both high and deep relative to the others.

What kind of router is that, and how has it performed elsewhere?
Author:  JRE Productions [ Mon Sep 08, 2008 3:24 pm ]
Post subject:  Re: strange second ledge using SM binding bit?
The bit is brand new (friday) and has only cut the pine LP blank for trial, a scrap pine board for depth adjustment and the archtop binding channels.

The router is an import but has been flawless. It runs better than my porter-cable laminate router and has no slop in the bearings. Right now I think it is either the bit or somehow my jig...but the jig only holds the router and goes up and down. Something is certainly not right though. Right now I wonder if the carbide tips are out of alignment with each other.

I saved the scrap piece. I will try to capture a picture of it.

Joe
Author:  Rod True [ Mon Sep 08, 2008 3:34 pm ]
Post subject:  Re: strange second ledge using SM binding bit?
As someone else said, shoot an email to Stew Mac and let them know the issue, they will send you out a new cutter ASAP. Those guys Rock!
Author:  Jeff Highland [ Mon Sep 08, 2008 7:49 pm ]
Post subject:  Re: strange second ledge using SM binding bit?
Joe, you mentioned you feel your rig is a bit heavy,
I am currently building mine and finding the same.
I am considering mounting a pulley and counterweight to offset the bulk of the weight of the router and lower the load on the guitar face.
Anyone done this?
Author:  PaulB [ Mon Sep 08, 2008 8:02 pm ]
Post subject:  Re: strange second ledge using SM binding bit?
I've had this happen too, but with a different bit, so I don't think the bit is the problem. My thought was that making multiple passes was the problem- after the first pass the jig indexes slightly differently against the guitar. I also used a different jig to you, and hand held job as described in the Williams book. Time to rebuild the jig IMHO.

I just go around the channel with a small chisel and chip out the ledge.
Author:  PaulB [ Mon Sep 08, 2008 8:34 pm ]
Post subject:  Re: strange second ledge using SM binding bit?
I guess I should be a little more specific...

If the jig is indexing off the top (or back) right on the edge of the top (or back), then any subsequent deeper cuts are going to index higher up on the dome of the top. This will lift the cutter higher on the next deeper pass, lifting it off the bottom of the channel you've just cut. Then you get that ledge you're seeing.

You need to modify the jig so that this doesn't happen.
Author:  gozierdt [ Mon Sep 08, 2008 9:01 pm ]
Post subject:  Re: strange second ledge using SM binding bit?
I agree with Howard and Todd. If you are creating this ledge in a single pass, then there is a problem with the
cutter- one flute is cutting further down and with a smaller diameter than the other.
Author:  JRE Productions [ Tue Sep 09, 2008 9:46 am ]
Post subject:  Re: strange second ledge using SM binding bit?
I checked my scrap test pieces this morning. They were straigh flat boards (Clear pine 2x4). All the cuts with all the different bearings caused the same ledge. There is no tapper/angle to the 2x4 like a top of a guitar, so there is no chance the the depth causing this. I sent a reply to SM from the shipping confirmation email they sent me. I will wait to hear thier reply. Most likely the carbide blades are not aligned correctly. I'll let you know what happends.

Joe
Author:  JRE Productions [ Tue Sep 09, 2008 9:49 am ]
Post subject:  Re: strange second ledge using SM binding bit?
Jeff Highland wrote:
Joe, you mentioned you feel your rig is a bit heavy,
I am currently building mine and finding the same.
I am considering mounting a pulley and counterweight to offset the bulk of the weight of the router and lower the load on the guitar face.
Anyone done this?


Jeff, I was thinking of adding a spring that would pull it upwards a little. But in all honesty, once I mounted the unit to my bench and once I made sure the carriage slid nice and smooth, the wieght was not terribly distracting. At least I know it was sitting firmly on the guitar top/back. It did not chatter or anything like that, so I think the weight is probably not a big issue after all.

Joe
Author:  Barry Daniels [ Tue Sep 09, 2008 10:53 am ]
Post subject:  Re: strange second ledge using SM binding bit?
Significant runout will cause the bit to wobble and leave a ledge like this. You just need to figure out if the runout is in the bit or the router. Should be easy enough.
Author:  Kirt Myers [ Tue Sep 09, 2008 11:54 am ]
Post subject:  Re: strange second ledge using SM binding bit?
Do you have a way to clamp the router in a vise and check the flutes with a dial indicator?
Author:  JRE Productions [ Tue Sep 09, 2008 1:54 pm ]
Post subject:  Re: strange second ledge using SM binding bit?
I certainly can do some more investigating on the router bit. I will probaby first do a visual on the two cutters to see if one appears shorter or higher than the other. I have several vises in the shop, so I can do that too.

I have not heard back from stew-mac yet, but has only been a day or so. So I will wait another day or so before calling them. I was able to bind #1, so I am not in a huge hurry, but don't want to be working on #2 before getting this resolved. I will also try placing a simular bit in the jig and see if anything strange happens.

J
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