rpms

[Mike Teachman]

Plunge routers and drill presses can both make holes. Why are drill press rpms so much lower?

[Tom Veatch]

The cutting geometry is different between the two. A twist drill cut is similar to that of a plane. It shaves a chip or "curly" off the bottom of the hole. If you look at a router bit capable of making a plunge cut, the business end encounters the wood more like a scraper. I suspect therein lies the reason for the different speeds at the cutting edge.

[Ken Fitzgerald]

I agree with Tom. I also think it has to do with the physcial size of the bit you might use. A 2" bit should probably be drilled a little slower than a 1/8" bit. The materials that might be drilled would have some effect too!....metal versus wood....

[Mike Teachman]

Theres overlap in the bit diameters and materials to be cut but not in the rpm ranges.

[Mike Teachman]

Whats better for the same size hole, a low rpm bit or a very high rpm bit?

[Steve Leverich]

Routers aren't made to drill holes in materials other than wood, drill presses ARE - if you were to try to run a 3/4" bit at 12,000 rpm while cutting a hole thru 1/2" steel plate it would likely make a small mark on the steel before needing to be replaced from having the edges burned beyond use.

Another thing - I wouldn't like to see what happened to a drive belt on a DP when trying to spin the quill @ 24000 rpm, especially with just that typical lightweight sheet metal cover over it - after all, it's usually right at head height :(

Third - ever try to use a forstner bit at even 3000 rpm? Good luck. First time I tried a fairly inexpensive forstner from a set, I thought they were total crap - mostly just BURNED their way thru the wood. Slowed down to about 500 rpm and magically, the bits became "good" again.

Finally, I think it'd drive the cost of a DP 'way higher to attempt a range of speeds from 220 to 22,000 - especially if using the typical 3-pulley, 2-belt system of most 12 to 16 speed presses.. Steve

[Steve Leverich]

Sorry Mike, was typing while you were - in wood, usually a higher speed is better for cleaner holes - a fast rpm with slow feed gives less tear out. But you can overdo this and cause burning.

For smaller holes, I usually use brad point bits at medium speeds (around 2000 rpm) with slow feed at first, for a clean entry hole - if both sides of the hole are important, a backer board will keep tearout from messing up the exit hole.

Generally - smaller hole, higher speed. This will also vary depending on the type of cutter, so you kinda need to experiment.

Metals - whole different deal, start over with the experiment :confused:

I typically use around 250 rpm on heavy (1/2") plate if the hole is bigger than about 1/4", with steel you're usually using a regular twist drill and should use cutting oil to help cool the bit - best to see a continuous "curl" of metal coming out of the hole. This way you know your bit is sharp and feed rate is optimal... Steve

[Mike Teachman]

Thanks, that makes sense.


Can you use a plunge router in aluminum or acrylic sheet or just wood?

[Steve Leverich]

The relatively high speed of even the slowest setting on routers would likely cause the bit to burn up in aluminum (especially some of the harder alloys) and in plastics you'd just sorta MELT your way through the material.

Do you have a specific project in mind, or just general knowledge gathering? Steve

[Joe Chritz]

I would suggest trying to find a copy of the machinist handbook, even an old one. It will list a huge range of cutting speeds for all kinds of cutter and materials.

For any combination there is an ideal sweet spot.

However, to answer your question generally faster is better to a certain point. Plus to further complicate things the ideal speed changes as the bit dulls. Rule of thumb is big bits are slow and small bits are fast. Hard material is slower than soft.

Plunge routers aren't really designed to drill holes, it just happens to work with a properly designed bit.

Also it is better to error on the slow side since you are less likely to loose attached parts that way.

Joe