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High rotational speeds

#260077 by rjent » Thu May 30, 2019 10:20 pm

When did the trend of 15000 and 20000+ RPM rotational speeds become "normal" and what does that speed do for us as wood workers.

I have my own theories and thoughts, but was just wondering how we collectively interpret the change from the earlier routers to the current ones.

I can get excellent quality cuts with a Mark V at approx. 6000 RPM while the PowerPro doesn't seem to really do any better at 9500 or 10000 RPM.

Since torque and RPM determine HP (Amount of work over time (550 foot-pounds per second)) and the faster the shaft spins the more HP is generated (assuming no change in torque). I suspect routers are turning faster and faster for HP bragging rights more than quality of routing.

What are your thoughts.

---

Dick

1965 Mark VII S/N 407684
1951 10 ER S/N ER 44570 -- Reborn 9/16/14
1950 10 ER S/N ER 33479 Reborn July 2016
1950 10 ER S/N ER 39671
1951 jigsaw
1951 !0 ER #3 in rebuild
500, Jointer, Bsaw, Bsander, Planer
2014 Mark 7 W/Lift assist - 14 4" Jointer - DC3300
And a plethora of small stuff .....


"The trouble with quotes on the Internet is that you can never know if they are genuine." - Benjamin Franklin

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Re: High rotational speeds

#260082 by everettdavis » Thu May 30, 2019 11:10 pm

20000 RPM on my 3HP Router is only applicable with small diameter router bits. My Freud raised panel cutter with a much larger diameter cutter area warns you to slow it down drastically.

One must exercise great care and develop discipline to dial back speeds when shutting down gear. Can you image what might happen with a grinding wheel or other abrasive not designed for those speeds on something capable of spinning that fast? I have cautioned more than one about using 5/8 11 wheels on angle grinders without knowing what the wheels were rated at.

I believe Shopsmith’s instructional guides tell us to take the machines to slow before turning them off for just that sort of risk mitigation. I sure don’t want to connect a bandsaw and have it come on at highest speed the headstock can run at.

Everett

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Re: High rotational speeds

#260083 by reible » Fri May 31, 2019 12:50 am

I expect that early routers were still pretty fast, that being in the 6000 to 8000 rpm range even back in the 1930's. They looked a lot different then what we now know as routes but functionally that is what they were. Keep in mind that the development of the router and the development of the router bit had to go hand in hand.

By the 1950's both bits and routers were able to run in the 12,000 to 18,000 rpm range. The faster speeds for smaller bits and the slower to larger bits.

I got my first router in 1976, a single speed running at 25,000 rpm and had only a 1/4" shank option. That speed worked well with the smaller bits but was limited due to shank size to mostly smaller bits anyway.

Now router can go from say 8000 to 32,000 rpm so effectively allowing larger bits to be used and with the shaft size of 1/2" some pretty large bits can be used effectively. The key is also that you can buy variable speed routers, so if 25,000 is to fast, not a problem just dial it down. You have a small bit crank it back up. You have the best of both worlds.

As an example say you want to use an 1/8" bit to cut a slot, it no longer matters you have all that horse power since it just doesn't need it and if you forced it then the bit snaps off. Here the rpm is much more critical then the power.

Bits have gone from steel to carbide and from single or two cutting faces to 3 and 4. They have also gone to a safety design where the amount of cut is limited due to the profile of the cutters.

Horse power while not a true measure has gone up a lot since the early days. How ever horse power has little meaning in that the modern router is unlikely to produce any where what the rating is and doesn't need to. The lone excepting to that is for very large cuts what need to be taken in a single pass. One major improvement in routers is the speed control that attempts to keep the set speed. On the older routers it was not uncommon for the motor to slow down as you cut, it may have said 20,000 rpm but under load that might well have been 15,000 or even lower.

In most cases smaller cuts are taken and multiple passes taken to achieve the desired finished results. You get very different results depending on how much material try to take off, just another factor among many.

What all this discussion keep in mind that cutting efficiency is speed dependent. The material, cutter design, sharpness and many other factors all add in. A simple way to see this is to take a router and cut the material you plan to use. Change things like speed, and feed rate or if you can even try a different bit to see what happens. Even the same type of wood can have different results depending on grain patterns and differing growth patterns. Let a bit get dull and see the difference that makes........ It all has to come together and when it does it is beautifully.


I personally don't like the results from the shopsmith, yes you can slow the feed rate down and all that sort of thing but who really wants to feed at half the rate you normally would with a common router? But that is not the main issue I have with the shopsmith as a router. Shopsmith just has never really gotten in to making the machine a router. You can't get things like guide bushings, the depth adjustment is clumsy at best and you have no fine adjustments. I could go on but I think it is best said that I don't often use the shopsmith for routing, there are just too many better ways to do the job.

I really wish that the powerpro had been designed to go from 100 rpm to 8000 rpm, I think it would have been a much better and more reliable machine.

Well a bit of rambling but routing is a passion for me. Lets just say I could use a different router each day of the a month and not have to reuse one during that time. I may have as much invested in router stuff then I do shopsmith stuff, with perhaps a slight edge going to shopsmith.

Ed

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{Knight of the Shopsmith} [Hero's don't wear capes, they wear dog tags]

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Re: High rotational speeds

#260087 by BuckeyeDennis » Fri May 31, 2019 7:07 am

One issue that I’ve never seen discussed in the context of woodworking is mechanical resonances. All structures, be they machine components or workpieces, have various frequencies at which they mechanically resonate, or “ring” in layman’s terms. The wooden bars on a xylophone are perfect examples.

When you cut wood with a typical rotary tool, the cutting action is discontinuous. There’s an impact every time a cutting tooth engages the workpiece. This creates a driving frequency that can excite those mechanical resonances. The driving frequency, in Hertz, can be calculated as Fd = RPM/60 * N, where N is the number of cutting teeth in one revolution. At 25000 rpm with a two-flute bit, for example, the driving frequency is 25000/60 * 2 = 833 Hz. If the driving frequency happens to be close to one of the mechanical resonant frequencies, you excite the resonance, everything starts vibrating, and the resulting “chatter” causes a rough cut.

In metal machining, this is a well-understood phenomenon. On a lathe, for example, if you get chatter, you either change your spindle speed to move the driving frequency, or maybe try to stiffen your tool mount to move the resonant frequency. I’ve personally seen a bell-shaped brass faucet component be machined with a beautiful finish at one spindle speed, yet come out looking like a pleated tin-foil Christmas ornament at a different speed.

For high-end metal machining, you can buy instruments that measure all of the resonant frequencies in the system. Then the spindle speed is calculated to place the driving frequency in between resonant frequencies, with no trial-and-error tuning.

So how does this relate to router speed?
1) At higher driving frequencies, you’re more likely to be above the fundamental resonant frequency of your workpiece.
2) With a variable-speed router, if you get chatter, you can simply change the router speed.

You can see the results of chatter as a rough finish. But you can also hear it while it’s happening. On a metal lathe, chatter typically sounds like a high-pitched shriek. When working wood, if the cutting action sounds unusually loud or harsh, you’re probably getting chatter.

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Re: High rotational speeds

#260088 by rjent » Fri May 31, 2019 8:32 am

BuckeyeDennis wrote:One issue that I’ve never seen discussed in the context of woodworking is mechanical resonances. All structures, be they machine components or workpieces, have various frequencies at which they mechanically resonate, or “ring” in layman’s terms. The wooden bars on a xylophone are perfect examples.

When you cut wood with a typical rotary tool, the cutting action is discontinuous. There’s an impact every time a cutting tooth engages the workpiece. This creates a driving frequency that can excite those mechanical resonances. The driving frequency, in Hertz, can be calculated as Fd = RPM/60 * N, where N is the number of cutting teeth in one revolution. At 25000 rpm with a two-flute bit, for example, the driving frequency is 25000/60 * 2 = 833 Hz. If the driving frequency happens to be close to one of the mechanical resonant frequencies, you excite the resonance, everything starts vibrating, and the resulting “chatter” causes a rough cut.

In metal machining, this is a well-understood phenomenon. On a lathe, for example, if you get chatter, you either change your spindle speed to move the driving frequency, or maybe try to stiffen your tool mount to move the resonant frequency. I’ve personally seen a bell-shaped brass faucet component be machined with a beautiful finish at one spindle speed, yet come out looking like a pleated tin-foil Christmas ornament at a different speed.

For high-end metal machining, you can buy instruments that measure all of the resonant frequencies in the system. Then the spindle speed is calculated to place the driving frequency in between resonant frequencies, with no trial-and-error tuning.

So how does this relate to router speed?
1) At higher driving frequencies, you’re more likely to be above the fundamental resonant frequency of your workpiece.
2) With a variable-speed router, if you get chatter, you can simply change the router speed.

You can see the results of chatter as a rough finish. But you can also hear it while it’s happening. On a metal lathe, chatter typically sounds like a high-pitched shriek. When working wood, if the cutting action sounds unusually loud or harsh, you’re probably getting chatter.


This sounds a lot like a marriage ... pitch, chatter, high-pitched shrieks, rough surfaces ... et al. :D

I personally am, in my humble opinion, getting good results on the shopsmith machines (what do I know LOL). Yes, I have a plunge router and it does an amazing job, but I still do a lot of raised panel doors exclusively on the SS. I have even done some of the center raised panels on a 10ER (large cutter) just for the hell of it and got outstanding results.

My question really stems from how much speed do you really need to get the job done, and are the router manufacturers just padding their stats with RPM.

Good info Dennis and Ed, stuff to ponder. Thanks

---

Dick

1965 Mark VII S/N 407684
1951 10 ER S/N ER 44570 -- Reborn 9/16/14
1950 10 ER S/N ER 33479 Reborn July 2016
1950 10 ER S/N ER 39671
1951 jigsaw
1951 !0 ER #3 in rebuild
500, Jointer, Bsaw, Bsander, Planer
2014 Mark 7 W/Lift assist - 14 4" Jointer - DC3300
And a plethora of small stuff .....


"The trouble with quotes on the Internet is that you can never know if they are genuine." - Benjamin Franklin

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Re: High rotational speeds

#260091 by sehast » Fri May 31, 2019 10:48 am

Most (but not all) router bits for wood between 1/8" and 1/2" in diameter are designed to run at 18000 RPM to accommodate feed rates from 30 to 90 inches per minute. That will usually get you a reasonably good cut with wood chips about the size of ground coffee. That does not mean you can't use a lower RPM but you will have to reduce the feed rate as Ed indicated to get the same size chips and quality of cut. I used the PowerPro with very large diameter bits, 1 1/2 minimum to 2+ inches for flush trim routing, rabbiting, etc. Basically any bit so large that I would have to slow my table router down to or below 16000 RPM to use. I feel I get better performance because the PowerPro has the horsepower to maintain the RPM through the cut and 10,000 RPM is sufficient due to the size and radial velocity of the bit that contacts the wood. Also using large bits with more flutes 3 or 4 instead of the normal two is a big performance plus. That is the reason shaper bits work as well as they do typically having 3 flutes and 2+ inch diameters at RPMs down to 7000.

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Re: High rotational speeds

#260093 by garys » Fri May 31, 2019 10:49 am

I have decided that you don't NEED the high speed, but it does make routing much easier with higher speeds. I've done raised panels on my Shopsmith and I've done them on my stand-alone router. The much higher speed of the router allows me to get a better job done faster and easier. I don't do any routing on my Shopsmith anymore.
I have two routers. The smaller one is used hand held and the larger one is table mounted. I don't NEED it that way, but I do WANT it that way.

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Re: High rotational speeds

#260095 by Hobbyman2 » Fri May 31, 2019 11:57 am

some times I believe we can get too critical and too scientific , JMO the first router was no more then a crude hand plane .
Most all router bits are rated at a max speed , as long as you are not getting chatter or burning my guess is life is good? JMO

---

Hobbyman2 Favorite Quote: "If a man does his best, what else is there?"
- General George S. Patton (1885-1945)

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Re: High rotational speeds

#260097 by Hobbyman2 » Fri May 31, 2019 12:22 pm

use the formulas below to calculate starting points for your test cuts.
https://www.freudtools.com/public/asset ... 170822.pdf



http://blog.carbideprocessors.com/uncat ... uter-bits/
If you are just starting out with woodworking, or maybe you don’t have a handy chart RPM nearby. There is an easy way to figure out the correct speed, or at least come really, really close, just by using your ears or by feel


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Maybe a digital rpm gage on the router would make some feel better , after all everything else is just a educated guess at best ?

---

Hobbyman2 Favorite Quote: "If a man does his best, what else is there?"
- General George S. Patton (1885-1945)

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Re: High rotational speeds

#260102 by lahola1 » Sat Jun 01, 2019 12:04 am

Thanks guys.
this is great information. I've always wondered exactly why high router speeds are better other than getting the job done faster.
I've found that with the simple routing/ shaping I do the SS works very well at 4000-5000 RPM and I don't need an extra piece of equipment (router table).

---

SS Mark VII(sn 405025), SSband saw, SS 4" jointer, SS Mark V 1980,
Smithy SuperShop 720, Craftsman RAS, Ridgid TS2412 Table Saw,
Delta 12" planer

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