Pattern routing problems

Jay Lock

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Hi everyone

I was trying to make a bunch of small cutting boards using a board that I made in 7th grade :eek: as a pattern. It is in the shape of a pig, so there are lots of turns etc and the pattern crosses the grain at different angles in the project.

Used double sticky tape to attach the blank to the pattern. I had cut it roughly to shape, about 1/8" larger than the original. I used a straight flush cut bit in my router table. Lots of tear out and a near accident, I wasn't holding down hard enough on a push pad and the router bit grabbed the piece and threw the whole thing off the table. Fortunately using the push pad kept my fingers out of the way.

No luck on the second one either, they both are in the trash. I can't find anything in my books that tells me what I'm doing wrong. Should I slow down the router speed? Should I be using a spiral bit?

Thanks for the help.
 
Sounds like, at different times, you were going with grain, cross grain and against grain, possibly with different woods too. The tear-out would have given me pause. Without being there to watch. I believe I would have gone to a quarter round bit, put the board on a non-slip pad and used the router instead of shaper. Glad you weren't injured.
 
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The bit in Allen's second link would work well for what you need to do. I haven't got one of those but I've had good success by cutting what I can with a bit with a bearing on the end (flush trim) and then switching to a pattern trimming bit to finish up. It's a slower way to do it but it gets the job done.
 
Thanks guys

I'm a bit confused! What is the difference between a pattern bit and a flush cut bit? The two bearings instead of one? Angled cutting surface rather than straight?

Dave -- Why to you go over the surface twice? I would think that the pattern cutting bit would create a part that was the same dimension as the pattern. So, what does going over with the flush bit add to the process?

Not going to play with that puppy today! I have to admit that I was surprised by how fast that wood was grabbed out of my hands, and so thankful that I wasn't holding it without a pusher pad on top. So, I'm cleaning up stuff and playing on the net until my hands stop shaking!

Jay
 
I've had small work "blow up" on my shaper...not an unexpected thing when shaping muntin bars for circular and elliptical windows. The spiral bits should help with this problem, but still make sure to keep your hands in a safe place. The spiral will cut with a shearing action rather than the blunt approach of a straight bit, kind of like slicing a turkey with a knife as opposed to going at it with an axe :)
 
Jay, I don't go ove the surface twice. I cut what I can cut without getting chipout with one bit--those areas where I'll be cutting without lifting the grain. Then I flip the work and template over, change the bit to the one with the bearing on the opposite end of the cutter and finish up those areas I didn't do the first time.
 
Jay,

My inexpensive flush trim bits have the cutter straight down the shaft. The Infinity double bearing pattern bit has the cutter slanted down the shaft. I do not know if it is how the bit is designed or if it is mainly the quality but the pattern bit sure cuts a lot better. I will mail mine over to you if you want to give it a try.

I think that the best of all worlds for a pattern bit in a table would be the downcut spiral flush trim bit which in a table would seem to be an upcut bit. That way, if you could attach the pattern tight against the workpiece, such as small nails, it would not splinter the non pattern side and the pattern would help it not splinter on the pattern side. I have not tried that as I do not have one of those bits (next bit to purchase) but I do have a couple of their regular spiral bits and they really cut smooth. Of course any of the top brands should be very good quality but I just happened to get started with the Infinity brand.

You are right about things happening really fast using a router. Faster than any other tool that I own. I think that is why that I always choose to hold the router instead of the workpiece if possible. Keeps my hands away from the bit. Doing something like a pattern on a table I use the Gripper. If I did a lot of that kind of stuff I would have two Grippers.

Be careful.

Allen
 
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I ran a test cut with my double bearing pattern bit and the results are below. I double taped a piece of MDF to represent the pattern to a piece of plywood to route the end grain where tearout would be if there was any. Then I set my router to the hightest speed. Made the cut using the starting pin just in case. I fliped the pattern and workpiece over for the first photo. No tearout and no grabbing equals no problem. There is a little tearout and the end of the cut which is to be expected with no backerboard but even at that it is not much, especially with plywood.

patternbit1.jpg


I separated the pattern from the workpiece and flipped over the workpiece. No tearout.

patternbit2.jpg


Here is a picture of the bit in my router and table. The bit's cutting length is two inches. A shorter one might be handier for most things as this is pushing the length of travel for my setup but works.

patternbit3.jpg
 
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Hi Jay,

A PIG board :D or a pig shaped board will have several areas where tear out is very likely to happen...Much like a guitar with its hourglass shape. Any place the router bit is pulling the grain open as it cuts (digging into the grain) will be a potential problem area...especially on quarter sawn boards. This is where the board will either be snatched from your hands or tear out. One technique I use is to examine the shape to be cut, determine which direction the bit will be rotating related to your router table and bearing guided bit and mark all the areas where the cut is pulling the grain apart or (biting into it). On these areas I use a climb cut and then finish off the piece by cutting all the way around with a normal "down hill" cut.

This is very easy to do and works very well...but is hard to explain. If it's not clear..let me know and I'll try to draw a picture. Or go here and look at page 14 www.stewmac.com/freeinfo/i-5295/i-5295.pdf

FYI - Depending on the type of wood you are using, I also suggest & agree with many of the other suggestions here....Take small nibbles...use a very sharp pattern bit. Spiral bits cut cleaner but I didn't know you could get them with a bearing??? Can you???

Also, depending on how "shaply" your pig is....it may be a good excuse to buy a spindal sander.:thumb:
 
another way to avoid tearout is to flip the board and pattern over....you`ll have to change from a top bearing bit to a bottom bearing but by flipping it over you`ll be able to route "down hill" to the grain on all the corners...
 
Something no one has mentioned is I would get as close as I could to the pattern because of all the grain problems. The less to cut the cleaner the cut.

I'll second this. Get within a 1/16th or less. Do you have a scroll saw, or if it is too thick for scrolling, a bandsaw with a small blade buried flush in a rounded point of wood or phenolic - this will follow a pattern template beautifully with zero chance of kickback or tearout. Depends on how intricate the pattern is. How perfect do these need to be? You'd be surprised how closely we can follow lines on a piece of paper from a printer or copier tacked to a piece of wood with fabric adhesive. Of course, I'm always thinking bandsaw. :rolleyes:
 
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