Router Bits


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Router Bits
Common ¼ inch shank router bits.
1/8 diameter shank bit
1/8 inch shank bits.
These are some of the woodworking bits that were used for the work shown on the Work Examples page.

They are primarily standard carbide ¼ inch shaft router bits. The double ended one is cheap high speed steel.

Suppliers include Bosch, Freud, Skil and MLCS.

A Skil ¼ inch straight bit, number 91103 from Lowes has been a handy low cost general purpose bit, though its flutes are only 5/8 inch long.

MLCS sells collet adapters that permit 1/8 inch bits to be used in ¼ inch collets.

Harbor Freight often sells a mixed box of 1/8 inch bits at a low price. These small bits work well in roto-tools such as Dremels. Some of the HF bits are in the second image.
 
Changing router bits during a job is a time consuming nuisance that introduces yet another opportunity for error.

Bits that can and cannot plunge
Left bit can plunge, right cannot.

To address this in this shop, bits and end-mills that are also capable of plunging are used for many jobs.
The left bit has flutes that meet in the center of the shaft, which will completely remove stock from a hole that is drilled straight downward.

The flutes on the right bit do not meet in the center, and the bit cannot plunge or drill straight downward. It will burn in wood and clog in aluminum.

Though the plunging bit can drill the stock, the drilling feed-rate has to be slower than would be permitted with regular drill bits. Overall, the slower feed-rate for the plunging move is still faster and easier than dealing with tool changes.

Straight flute bits are not as effective at removing chips as spiral flute bits, and in deeper cuts the chips can clog the bit and ruin a job. Altering the feed-rate and keeping the cut area clear can help to remedy this.
 
Milling Aluminum

Aluminum can be milled with all of the Solsylva CNC machines that have supported rails. These are the 10x9, 18x24, 25x25 and the 24x48 machines.
The unsupported rails of the 13x13 permit too much flex to work well with aluminum.

Aluminum can be milled with regular carbide flute router bits.
End-mills for milling machines can also be used.

Aluminum stock has to be removed more slowly than wood. This is accomplished with shallower passes and slower speeds.

Smaller bits, e.g. 1/8 inch, also remove less stock per pass, but small bits are not as forgiving as ¼ inch bits, and are prone to breaking with the slightest misstep.
Larger end-mills (over ¼ inch) generally require more force than these DIY machines can deliver. ¼ inch is an easily found size that has served well.

Generally, the practice in this shop is to create the g-code at 0.02 to 0.03 inch of stock removal per pass with a feed rate of 25 inches per minute. The router's spindle speed is left at its normal rpm, (~30,000).


It is easier to speed up the feed-rate to ~40 ipm for example, than it is to re-code the depth of cut per pass.
Hitting the increase or decrease feed-rate override keys in Mach is an easy way to quickly reset a too slow or fast cut.

Ramping into a cut is preferred over a straight down plunge, but this move can be challenging to g-code with lower end software.
This can be addressed by slowing the plunge feed-rate. 8 ipm has become the default rate here with ¼ inch center cutting bits and end-mills. For thicker stock, a chip clearing retract move is helpful. This can be hand edited in the g-code as a simple Z G01 move rather than as a G73 peck drilling move.

It is important to keep a close eye and ear on the work. Small bits and end-mills can clog and break quickly. Hitting pause, and stopping the spindle at the slightest bogging-down sound can save a job, and yet another end-mill. The job can be continued after the bit/end-mill is cleaned and the feed-rate is altered.

In short, shallow passes are a good start, feed-rates can be changed on the fly.
 
Here is a center-cutting spiral flute end-mill. It can also double as a slow plunging drill in aluminum. The spirals help to lift the chips from the cuts and holes.

An end-mill that has served well here is a solid carbide, double end, two flute, ¼ inch shaft, Atrax part number A9404490. Use-enco.com is an online supplier. This double ended end-mill is long and may not fit in all router collets.

Atrax end mill
Spiral flute end-mill.
 
Clogged Endmill
Clogged end-mill.
This shows what happens when a dull bit or end-mill is used to machine aluminum. A too high feed rate will do the same.

The aluminum clogs the flutes and prevents the tool from cutting the stock. The metal melts and bonds to the bit.

The chips are also pressed into the sides of the stock as shown below. The process rapidly deteriorates, and the job is ruined by excess chatter.
 
The last two images show the difference between cuts made with a dull bit and a sharp one. These were milled in the same stock on the same machine with the same speed and depth of cut.

Results of clogged bit.
Aluminum milled with dull bit.

Aluminum milled on the 10x9 with precision Acme leadscrews.
Aluminum milled with sharp bit.
 
There are a number of ways to prevent the chips from accumulating and clogging the work.
  • Keep the bits sharp.
  • Use spiral flute end-mills.
  • Make many fast shallow passes, rather than a few slow deep ones.
  • Use compressed air to blow the chips from the holes and recesses.
  • Use a vacuum to draw the chips from the work area.
  • Make peck drilling or retract moves while drilling.
Flood cooling and chip removal are used in metal working operations, but with DIY wooden machines the liquid coolant is impractical.

Compressed air is a workable alternative.
The pressure and volume do not have to be high to be effective. Pressures as low as 20 psi have served well here when the air jet is aimed directly at the end of the bit.

The low air volume and pressure permit a small low cost compressor to do an adequate job.