View Full Version : Edge finders and techniques.

01-04-2005, 11:09 AM
Just looking for advise on finding an edge and aligining the stock on the CNC router table. What do yo recommend?

Do you use an edge finders to find the edge or do you use another technique?

My wood stock is typically not parallel sometimes because all I am doing is cutting INTO it.

01-04-2005, 11:20 AM
That's a great question, I to am in the process of using my new cnc mill and was wondering the same thing. I know with the software I'm using I can jog the machine with a edge finder on it and once the end is found I can simply zero out all the axis and than run the part. This only if the part I'm making need a reference, otherwise I could just to the looks about right method.

01-04-2005, 11:42 AM
I use them all the time. Run them about 1100 rpm. Some software will compensate for the dia, some won't. Edge finders will get you to within ±.001 or closer when done correctly.

Other methods I've used, (some not safe and I'm advising you NOT to use them), are to position a sharp tipped tool, angle cutter, center drill, or even a scribe held in the spindle, and eye-ball it so it's close. You can get to within ±.015 or better this way.

You can program a non-rotating tool to come down to position the part, using the machine/program to locate with, (aka a tool stop or drop stop).

You can take an end-mill, rotating at about 300 rpm, and hold a strip of paper between the end-mill and the part, and jog up 'til it pulls the paper out of your hand. (I DO NOT reccomend this method, as it involves getting your fingers close to the tool) This method is good for ±.003 or so.

01-04-2005, 11:54 AM
I bought one of these fancy red LED edge finders, thinking this would be easy to see when the lights come on. Surprisingly enough, the light is practically invisible at a decent speed.(I'm not working in the dark, though). I find I can only run it about 200 rpm. I have another type which is just a mechanical one, but it has a flat spot on the cylindrical end, so it clicks when it jumps. This is convenient for situations where you cannot see the regular edgefinder move so well (in Y, for example).

01-04-2005, 12:02 PM
I use the CNC router to cut the fixture stops. That way I know that they are straight to the axis. Then I just have to lay my wood part up against the stops and I know its straight.

Otherwise, if my wood part is oversize and the edges aren't straight, I simply eyeball it on the table and clamp it in place. Sometime I cut the outline of the part into my spoilboard, just so I know exactly where the program will cut.

01-04-2005, 12:12 PM
I bought one of these fancy red LED edge finders, ... I find I can only run it about 200 rpm. ...

I've had a couple of those, and always ran them without the spindle turning. Was yours designed to be turning while in use?

01-04-2005, 12:14 PM

Thanks guys. This is why this forum rocks.

I really like the paper technique!! ;-)

A couple of questions:

1. ALL| How do you guys get your router speeds down so low? I think my Porter Cable 690 has a range of 10,000-27,500 rpm.
2. BUSCHT| Do you clamp your jig down , visually aligned, and then let the machine cut the stops, channels? Are the stops removeable, if so can you re-align them or do you just start over?

I am setting up a jig with pegs for making guitar bodies. The jig will let me carve each side while keeping it aligned. The trick is drilling the holes on each blank before putting it in my jig. I could do it by hand, but I would like to have the CNC drill the holes, then place the the blank on the jig to begin routing.

01-04-2005, 12:50 PM
Most of the guys using edgefinders are cutting metal on a Bridgeport milling machine with a lower RPM than a wood cutting router.

I think I understand what you are trying to do, but not 100%.

To answer your question, What I have done on my machine is to use the machine to cut its own table top. I have have a stop rail in the X and Y that I cut square to the axis. All spoil boards or jigs are positioned up against the rails and either clamped or screwed in place, depending upon my mood/ or how the jig is designed.

I would then cut the jig on the router so its perfectly square also. Anything like peg holes would be put in then so I know that they are correct.

If I understand your application, you are drilling two holes to use with alignment pins to keep front and back milling in line. It would seem to me that the two holes need to be accurate with respect to each other, but they only need to be visually straight with the wood grain and centered good enough so you have excess material on all sides.

If that's correct, then all you have to do is cut a guitar outline on the table bed and place your rough part over this, making sure that the rough part overlaps the outline on all side and the wood grain is visually lined up. You could get a cheap laser level light to help with this. Fasten it to the gantry and have it shine down parallel across the two drill holes.

You idea of the pins should work well for alignment.

If I'm way off here, post a sketch if you can.


01-04-2005, 01:31 PM
Thanks BUSCHT,

You are right in linw with what I am wanting to do!

What do you make your stop rails out of? MDF, Hardwood?

What do you use for your table top? MDF, with laminate?

With your Idea, I am also thinkng of using the machine to cut channels in the table top for inserting T-Slot track.

01-04-2005, 02:08 PM
My table top is made out of Baltic Birch plywood, but MDF would work as well. I don't personally like using Plastic Laminate. Its kind of slippery and hampers clamping efforts.

I cut the table top flat then screwed additional baltic birch pieces for the X and Y rails. I then use the router to square up the inside edges. Some guys drill holes and use pins for the stops. That way they are removable if you want to do something else.

I agree with using the machine to cut the T slot channels. I've seen people surface cut the table, cut the T slot channels, vacuum lines, and locating pins with the machine. Its hard to beat this method for accuracy.
Good luck

01-04-2005, 02:13 PM
what do you use to surface cut the table? A facing mill?

01-04-2005, 02:18 PM
At work on our large 48"x120" routers we would use a flycutter.

At home on my small 12" x 12" bed, I just use a square router bit and take lots of passes.

01-04-2005, 02:22 PM
I've had a couple of those, and always ran them without the spindle turning. Was yours designed to be turning while in use?

Maybe you're right. The unit I have has quite a stiff "finger" on it, but it will move if you push hard on it.

But, it would be asking a lot for the finder to be perfectly centered just by throwing it in a holder. So a slow rotation will bring it in and out of contact until it actually contacts continuously. When the 4 leds just begin to stay light continuously, I call that edge "found".