Preventing router burn

[Arron]

Hi,
I need to do a large number of cuts with a router. Its on a router table, and I'm pushing the timber into a straight bit, then retracting it, to create U shaped holes in the edge of the timber. The router is a powerful makita without variable speed. The problem I have is the router leaves the hole burnt and discoloured. I know that retracting it instantly would minimize the burning, but I have a safe way of doing this and it doesnt allow me to do anything quickly. Are there any other ways of preventing router burn ????

cheers
Arron

[Chief Tiff]

What size router bit are you using? If you're trying to cut 3/4" wide grooves in one go at high speed then burning is going to be a fact of life. Not having variable speed is a huge disadvantage but there are a couple of ways around it such as using a smaller diameter bit and doing two cuts (one for each side), or using a smaller bit first then the larger size to clean up both edges together, handy if you are using a jig which "traps" the workpiece.

Lastly, how sharp is the bit? A top quality bit such as CMT or Freud will certainly help and to be honest the price difference isn't that great. I started out using El Cheapo sets, then progressed up to Carbi-tool and Linbide but for my commonly used bits I only use CMT now. No burning, clean edges and practically no sanding required!

[Arron]

Thanks for the response. Its hard to explain what I'm doing so I've drawn it. I'm not actually cutting a slot, more a matter of putting notches on the side of pieces of timber. Each one to be 12mm and perfectly shaped. Thats why just plunging it onto a 12mm straight bit gives me a perfect cut, except for the burning. When the piece is finished, the timber is viewed from the notched side, so the burning is immediately visible and unacceptable. I have quite a lot of these to do.

The sharpness of the bit could be an issue. It is a quality bit, not out one of those cheap sets. However I have others which I could try later. I find it hard to judge a router bits sharpness without actually using it and comparing.

cheers
Arron

[Chief Tiff]

Hmmm,

Maybe one of those solid carbide bits that have a spiral flute? They are supposed to run a lot cooler as they shear through the wood fibres as opposed to chopping through them.

[ian]

Arron
do those notches need to be a perfect half circle?
if not, an alternaate method is to drill a 12mm hole down the centre of the wood and then cut the piece into two halves

[A Duke]

Hi,
How about passing it side down over a 1/2" core box bit? You could clamp them in a stack with a piece of scrap last to take care of tear out.
Regards

[Ian Smith]

......... but I have a safe way of doing this and it doesnt allow me to do anything quickly. Are there any other ways of preventing router burn ????

Arron,
There's yer problem right there!!
If you are easing the bit into the cut slowly it will burn, especially. in your case, the sides where the bit remains in contact with the work the longest.

I've just come up from the shed having dealt successfully with exactly your problem. Well, not exactly, but router burn nonetheless.
You have to keep the work moving, once you hesitate, or move it too slowly it'll burn.
I would suggest short sharp, and small nibbles at the job you are doing.
If you just commence the feed and keep it going to full depth in one hit you 'll get burning sure as eggs.

Or you could try a Forstner bit and mill the holes

Ian

[joe greiner]

Have you tried taking smaller nibbles instead of cutting all at once? Re-setting the fence for nibbling each time would be a nightmare, but you could sneak up on it by placing shims on the fence, and removing them in sequence. For position control, clamp a stop block on the fence. Depending on the number of slots, their locations, the number of boards, and the number of shims/nibbles, establish a working order that minimizes lost motion and/or resetting the accessories. A written checklist will help a lot. And only the last nibble will need exquisite handling, more or less.

Cheers,
Joe

[bookend]

You haven't said how thick the piece is that you're routing. If it's thick and you try to do the whole depth at once, you'll go slower and burn more. Try adjusting the height of the bit to only take a few millimetres at a time.

Set up the routing with a right angle push fence that runs along your normal router table fence and stops clamped to your normal fence so that the sliding fence can only travel to the distance you want.

[Cruzi]

3 things create router burn, router speed, cutter sharpness and feed speed.

Since you have decided to use a fixed speed router (not the best idea in a router table), changing router speed is out.

To compensate for the fixed speed is often best to feed workpiece through faster (or slower, depending on issue),to compensate, try making a right angle holding jig type thingy to quickly feed it in and out.

Straight flute cutters are a mugs game, once you start using spiral cut solid carbide bits you will wonder how you ever went without them, if however you need a fixed diameter larger than 1/2", ie 3/4" you are stuck with either straight flutes or one of the suggestions above.

Blunt bits burn, (love illiteration :U), use a new bit or if workpiece thickness permits, try using less used areas of the bit ie closer to the shank.

HTH

[Harry72]

Like the others above said do it in at least two passes a 12mm radius is a fair amount to remove in one pass, the speed is fine a 12mm round flute bit is small enough for high speed.
On the final pass only take about 1mm off.

Are you doing the flutes stopped, like finger holds on a draw? This can be done in several passes.

[Arron]

Yesterday I got some shed time and retried this.

I stuck a new router bit in. It isnt particularly good quality, just what I could find in the shed, but it appeared to be unused. Doing it in several passes doesnt make much difference. The final pass was removing 2 mm and the burn was much the same. I tried dampening it with water too, but that didnt make much difference either.

The problem appears to be the delay in retracting the work. It dwells on the router bit for a while (like 1/2 second) and that is what does the damage. Holding it in such a way that I can retract it quickly puts my fingers too close to the cutter for comfort. Perhaps I need to make a jig that will allow me to manipulate it better.

Also, I suspect the spiral bit will do the trick - I should purchase one of them when next in a ww shop.

I hadnt thought about router speed. I do have another router, which is variable, so I will try that too.

I expect one or a combination of these will nail it.

cheers and thanks for the advice
Arron

[ian]

Arron
you haven't said how long each piece of timber is, or how closely spaced the notches are, or how your router table and fence are setup

armed with this info -- maybe post some photos -- the collective brains trust may be able to suggest a method and/or jig that is safe for your fingers (and other body parts)