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brucet999 08-12-2020 07:24 PM

router spiral bit grabs, ruins cut
I am making small sliding lid jewelry boxes for Orange County Toymakers charity. Using a solid block 2" x 3" x 1 1/2", I hog out the inside and cut for a dovetail sliding lid. My problem is that the 1/2" up-cut spiral bit, as I run into the corners sometimes grabs the grain in two of the corners and drags the bit/router body outside the intended cut line. I am moving the workpiece upside down counter clockwise within my jig, so against the rotation direction of the flutes. I tried once to do a climb cut, but got the work taken out of my hands an flung across the shop, so I am leery of that approach.

Here are pics of my jig, the workpiece before routing, and two with damaged corners.





Can anyone tell me how to avoid that corner tear-out?

difalkner 08-12-2020 09:58 PM

How deep of a cut are you taking, Bruce? Is it possible to do the cut on a larger piece and then cut it down to the size you need just to be safer and have more to hold for the cut?


Dave McCann 08-12-2020 10:26 PM

Maybe this will work for you?

MLCS 7488 1/2-Inch Diameter Solid Carbide Downcut Spiral Router Bit
Image result for MLCS 7488 1/2-Inch Diameter Solid Carbide Downcut Spiral Router Bit
MLCS solid carbide spiral bit. 2 flute flat bottom cutters. Top quality micro grain solid carbide. Down cut spirals help hold the material in place while using handheld routers. Will plunge cut and plane edges. Eliminates chipping at the top of the cut. Ideal for soft and hard woods, plywoods and composites, laminates, plastics and some non-ferrous metals
Technical Details
Manufacturer MLCS
Part Number 7488
Item Weight 3.2 ounces
Package Dimensions 2.8 x 0.8 x 0.7 inches
Item model number 7488
Material Carbide

Dave McCann 08-12-2020 10:36 PM

1 Attachment(s)
Maybe drill the corners out (undersize) before drilling the center areas? Leaving less in the corners for the router bit to remove.

brucet999 08-13-2020 01:59 AM

The wood is not moving into the bit, but is held tightly to the side of the jig. It appears that the bit is dragging itself beyond the limits of the jig by as much as 3/64". As that corner of the work (and to a lesser extent, the opposite corner) moves into the bit, there is a lot of vibration and noise, The result is the cut not being straight into the corner, but veering outward. Note that the other corner on the same side is nice and straight because the work moves across grain on the short side into that corner, then works its way out along the long side.

brucet999 08-13-2020 02:05 AM

I suppose I could drill the corners before hogging out the center with the Forstner bit, but that would treble the work time of that step and require another setup. This is not a one-off item. I'm committed to make a couple hundred of these little boxes in batches of 24 to 30 at a time.

I'm hoping to find a simpler solution, if I can.

brucet999 08-13-2020 02:14 AM

The problem is not chipping at top of cut. Note that the second picture has no chip out but both of them have corner cuts distorted. Any chip-out disappears with the next step of cutting with the dovetail bit for the sliding lid track.


I cannot imagine how to use a moving router on a 2" x 3" work piece with any accuracy at all.

On the router table, a down-cut would tend to push the work up out of my jig, making it twice as difficult to hold the work, and it would still have the problem of grabbing the grain going into those two corners and distorting the cut.

brucet999 08-13-2020 02:31 AM

Thank you all for offering your help. Here's a little more information.

I am running the bit at the manufacturer's recommended 16,000 rpm. If the bit is grabbing wood grain as it progresses (relatively, of course, since actually the wood is moving over the bit) in the direction of the grain into the problem corners, would higher rpm help or make the problem worse?

I suspect that a climb cut along the short, cross grain side into that corner might not let the bit grab the grain, but I am not strong enough to keep it from terrifyingly ripping the piece out of my hands.

TimPa 08-13-2020 06:51 AM

your project is fraught with risks, because of the depth of cut required, just removing too much material. a down cut will minimize the tearout at the cuts edge for sure. but, i highly recommend you find a different approach to the box. or buy a small cnc.

woodnthings 08-13-2020 08:15 AM

I'll try to explain this approach .....

This is on the right track. You need a large area around the block to support the router base. You do not want to hand hold the workpiece for this!

You need to secure the block after you drop it into the opening which is made very precisely to fit. A threaded insert and rod the clamps the block in place ..... maybe two, one on each side at 90 degrees?

The top of the block must be flush with the larger surrounding area.
A rectangular frame/jig is attached to the "surround" to limit the router travel such that it creates the desired opening in the block.

Assuming your router base is round will make that easier. Two "L" shaped pieces can be adjusted to create the jig.

Once the block is secured inside the drop hole and the jig is screwed to the surround, you can begin with a shallow cut like 1/4" or so, moving the router inside the frame in the correct direction. This first cut will minimize tearout. Then you can make a second or third cut down to final depth.

You will not be hand holding the block which is totally unsafe. The drop in jig will secure the block well enough to permit the router to cut smoothly without vibration. This is critical. The jig is much like a milling vise on the vertical milling machine which can take very strong cutting forces in metal. The first cut it also critical for a clean result. Adjust the depth to get the best result.

Actually, a small vertical mill with a CNC control would eliminate the router altogether, but I don't think the RPMs would be fast enough for a clean cut in wood. A CNC router is the perfect method as suggested above.

Another approach is to bandsaw out the center opening by making an entrance cut for the blade and then gluing it back together. This would require a separate bottom also glued on afterwards.

If only you could "mold" wood in a press like plastic injection molding, this would be a perfect application. :vs_cool:

Tool Agnostic 08-13-2020 09:48 AM

First and foremost, thank you for your hard work and contributions to the Orange County Toymakers program, especially during these challenging times.

You mentioned your concern about the downcut spiral bit, but have you considered one of the new(-ish?) "compression" spiral bits? They are also known as "up/down" spiral bits. I have never tried one, but they "upcut" in the bottom and "downcut" at the top.

MLCS #7425 is their 1/2 inch version:
(Scroll down, #7425 is near the bottom)

Here is a Whiteside version:

TimPa 08-13-2020 11:11 AM


Originally Posted by woodnthings (Post 2128273)
Another approach is to bandsaw out the center opening by making an entrance cut for the blade and then gluing it back together. This would require a separate bottom also glued on afterwards.

great idea!!

DrRobert 08-13-2020 11:16 AM

Definitely down cut/Plunge corners first/Be sure everything is solidly held in place/Go slow.

TomCT2 08-13-2020 12:27 PM

"...but I am not strong enough to keep it from terrifyingly ripping the piece out of my hands."

how about a big plate with a cut out/hole for the work pc, perhaps some wedges or side clamps to keep it tight, plus knobs/handles/grips.

give you a big chunk-o-wood to hang onto, and gets your fingers away from the bits that bite....

JohnGi 08-13-2020 02:48 PM

woodnthings andTomCT2 are steering you in the right direction. Cutting force is controlled with mass, rigidity, and leverage. Hand holding a small workpiece gives you none of these. As Tom says, this small workpiece should be securely held by mechanical clamps in a large, heavy fixture with solid, comfortable handles spaced widely apart. I also like to have a table pin 6" to 12" from the spindle that one edge of the fixture can slide against. On a shaper these are sometimes called starting pins since they are so useful in plunge cuts which are especially prone to kickback. Used as a fixed fulcrum they greatly increase control at moments when the movement of the workpiece against the cutterhead must be smooth and unwavering.

moosie 08-13-2020 02:53 PM

It's risky holding that tiny workpiece with your hands.

I'd start by hogging more wood, and just use the router for cleanup. And then, limit depth to 1/2" at a time. The router won't crack a sweat.

Then, I'd make an upside-down sled. A piece of baltic birch, 4-5x the length and width of the piece. Lay the workpiece near the center, and immobilize it with four short hardwood cleats screwed to the sled. Short so they don't hit your fence...

Now, flip the whole thing over, placing the box inside your fences. There will be a couple of handles on this "top" side. Your down pressure will keep the box forced against the table, and tight to the sled in the vertical direction.

At this point, with the piece quite stable, and your hands 8" or more away from the bit, a climb cut should be no problem - especially with pre-hogged wood, and limited depth.

I don't think it's your problem, but a bit of masking tape on the corners can help with any surface chip out.

I think the stability will eliminate chatter, and the 'drift' you were seeing.

Placing each successive workpiece in the sled may not require any moving of the cleats. If your tolerances are close, use some chopped up playing cards for shims to wedge it in.

brucet999 08-14-2020 12:35 AM

Moose, I think I can visualize part of your "upside down sled" idea, but 5 times the length and width would make it a 15" x 10" sled.

The hardwood cleats idea makes no picture in my mind. How would I hold the box on the under side of the sled?

With such a big sled, how would I see to place my box inside the jig? As it is, I have to pivot the piece a little while putting it in the jig so as to gently plunge the bit into the bottom of the box. taking off 1/32" of material to smooth out the forstner bit grooves.

brucet999 08-14-2020 12:55 AM

Could that sled/holder be made in two parts, each part with two cleats forming a corner? If there were a bit of a gap between the holder halves, with some sort of clamping mechanism (ideally a quick connect, eccentric cam lever) to try to force the corners together against the corners of the work piece, it would be held tightly. A handle on each half would give me a firm grip. What do you think?

Still a visibility problem, though.

NoThankyou 08-14-2020 01:30 AM

A VERY dumb question here.

Have you tried moving the router in a clockwise direction?

fareastern 08-14-2020 04:13 AM

I have a horrible feeling that continuing to make these items in the same way will one day lead to a post regretting your ability to count to ten has been seriously impaired.If I had to make them I'm fairly sure I would do it by making a router jig for use with a guide bush and would do it with the stock in a length that would yield several parts and cross cutting them after routing.The jig-and stock-would be clamped down to the bench securely and I would use the depth stops on the router to allow several passes.I would also tend to use a straight or downcut tool.I have never yet used a compression tool with a hand held router and wonder whether the considerable cost would be justified.
The alternative of a fixture on a CNC router would also be very good,just as long as you have such a machine handy.

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