Routers

[Michael Campbell]

I have a Makita Plunge router.  Had it for about 7 years and it works good..  On the router it has a speed control and I do not know what it is for.  When would I want to slow the speed of my router down.  I think it might have something to do with friction so I don't burn up the bits, but how do I know what speed to run? 

I always run on high by the way.

[John Schaben]

You slow it down to prevent burning, the wood and the bits. The other reason  is for safety, manage the tip speed by slowing down with the larger diameter bits. Here's snap of a chart published by MLCS. There are other charts around that may vary a bit but this is a good guide.

[mo khan]

Yeah John is right- I have a Makita router too and when i use it in my makeshift router table with large bits (like a panel raising bit) i slow the speed down and move the workpieces slower too!

[Jay Boutwell]

Hello Michael, Normally I never worry about speed as much as I do with the rate of feed and the debth of the cut.   I do however worry about it when I turn such things as a very large 3 1/2 " bits like the panel raising bits in the table router.  With the large bit the increased speed on the rim of the bit results in excessive viberation and pressures  which as one can understand  the results of a hunk of carbide flying about in the shop.  You think a table saw kick back is bad the flying sharp fragments of a router bit is more like that of a bullet. 

You are correct in the burning of the wood and heat of the bits but you must also consider that of the pressures exerted and the heat generated on not only the cutting head of the bit but that of the shank as well. 

In my work I use many types and sizes of bits and cut many different woods, cutting from raised door panels to the groove or channels for an inlay.  Some of these woods are extreamly hard with not only straight grain but also with wild interlocking grains with fibers that resemble a ball of string when cut.  In order to accompolish this I have several things to consider and they all differ depending on what type of cut it is, the type of material, and type of bit you  need to use.

In making the cut the best method of determining speed of the bit and rate of feed is sound.  The best method is to cut with the highest bit rpm that  yeilds a constant decible of sound yet making a clean cut that resembles a shaving rather that a chip.  You will need to adjust your rate of feed and depth of cut to prevent burning of the wood and producing chips and tear out in the wood.  Burning is usually due to dull bit or running too slow both in rpm and rate of feed.   When there is a resulting chip and tear out out the bit is dull or the cut is too deep or  the router in being pushed so that the bit if lifting the grain.  ( the wrong direction of travel  for the wood grain.)

You consider the direction of wood grain and  when possible avoid cutting into the wood where you are lifting the grain when the cut is made.  Try to lay out the routing project so that when routing, the router  bit is entering the wood and the bits rotation is in the same direction as the wood grain is running. ( avoid lifting the grain fibers up off the wood as the cut is made, cut with the grain and not against it.)  Do this by wood selection and lay out of the project and not by the direction you pust the router across your work.

You must use extreme caution here and besure to run the router so that the cutting edge of the bits enters the wood  against that of the travel you are pushing the router.  It is dangerous to run the router in the direction that of the bit rotation as it will grab and run away from you.  This can not only ruin the piece you are routing but can also lead to personal injury to yourself or a by-stander. 

 The best example here is to imaginge cutting the outside of a square frame. You would lay the frame out  face up and with the frame in front of you place the router at the lower right corner and turn on the router and push it forward and continue aroung the frame in the same direction.  Since your router bit is turning is a clockwise direction you are pushing the router is the direction that causes the bit to enter the wood in a direction that is against that of your push as you feed the router around the frame.

  There will be times when the grain of the wood will not cut cleanly and thus will call for the dangerous method in which you are moving the router in the same direction as that of the bit rotation.  Other wise is it just opposite of that as described in the cutting direction of the frame above. This is known as a "climb cut" and at no time should this be done if it is possible.  If it a "must do thing", then by all means do not make a deep cut as it is just too dangerous.

I try to prevent the need for climb cutting by laying out the wood stock so that the grain will be such as I am not cutting against the wild grain and often this is the matter of flipping the wood end or end and or over depending on how the grain runs.  If it is too wild of a grain and does not present a good view then either pick another piece or use a trick I often use.  I will take a common wood chisel and make a series of cuts directly into the wood edge that I am going to route.  This tends to relieve the chip out allowing the cut piece to break off before it splits out into a large chip out.  I will in this case take very light cuts until I have finished the cut.

I recently had the fortune of testing a set of rail stile bits for a company of which has elimated the frequent chip out and tear out of the wood fibers in cutting a stile or rail for a door.  For anyone whom is interested I do have the results of these tests as well as the source of these bits.  The same company also makes a full line of excellent bits that are actually better than the many others that I have used.   Contact me should you be interested. 

From the many thousands of cuts I have made with a router I can tell you that this is dangerous if not done properly and percautions taken to prevent accident.  Part of the this is the importance of thinking out what you are doing before the bit hits the wood,  wear protective devices such as a good set of shatter proof glasses and use bits that are sharp and absent of any defect.   A good set of bits is a necessary part of this remaining an enjoyable and or profitable  venture.    

 

 

 

[John Schaben]

Nice write up Jay - as usual, every point dead on... The only thing I would add is to treat extra long/tall bits the same as large diameter bits. I have some with cutting lengths of over 2" that get reduced speed. Again, your point about the sound being the best indicator. Personally, I'm not a proponent of running the things at full speed. It allows me to slow down my feed rate to a comfortable pace without getting into heat issues.

 

PS - I may be contacting you about the source of those rail/stile sets. Would be most interested in the test plan and results

[Michael Campbell]

Thank you very much John, Mo and Jay..  I was asked the question yesterday by an employee that i set up on running a Bead Bit for some 3 pc. Base trim i am working on.  I was never sure so thought I would ask the most talented friends I have.  I do have a better understanding so thank you very much.  I was told about 20yrs ago by an old timer craftsman to be careful of the router, said it is the most dangerous tool in the shop.  And you expressed the danger of it also Jay.  The router sent me to the emergency room about 7 years ago. ran a 1 1/2 inch flush cut over my wrist while i was doing some returns on an open stair case.  So I now respect the router.  But every time I hear it start up I feel the nerves on edge.  Again Thank you for the help.