General router question

[sdantonio]

I was poking around on the Nook Industries site the other day running a few numbers through their ball screw lifetime calculator and it got me thinking. When they asked for “how much force will be applied to the screw” I just faked in and put in 25lbs.

If you’re running a 2.25hp router at about 40-70ipm taking 1/8 inch cuts with a ½ inch bit, does anyone have a feel for what the right number would be for the force this would generate on the screw? Of course there is also the momentum from the gantry too.

The lifetime calculator, using one of their least expensive screws came up with 12 million inches of lifetime for 25lbs force. And at my rate of use that is something like 23 years.

Is that even remotely realistic?

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[ger21]

With a sharp bit, cutting a softer wood (like poplar), I'd say maybe 5lbs max. And with a really dull bit cutting maple, I'd still say much less than 25lbs, even if the bit was so dull it was smoking.
40-70 ipm is slower than a lot of hand routing, if you think about it. And again, a lot of times you'll remove more material than 1/8" when hand routing? Have you ever put 25lbs of force on a handheld router. Maybe, but not often.

A general rule of thumb I read a long time ago was to figure 30lbs of force. I like to say 30-50lbs to be on the safe side, but on average, I'd say more like 10-20lbs. Depends on how much the router can handle. With the right tooling, like chipbreakers or roughing bits, you can take deeper, faster cuts without putting more load on the router. They'll cost more, but they'll also let you get more out of your machine.

I really need to get my machine done so I can have some real world numbers to back me up. Just to make sure that using 10HP routers all day isn't skewing my view of reality.

On a somewhat related note, or maybe not related at all, I see a lot of people worried about going too fast and breaking bits. Our router at work uses aluminum based pods, on linear shafts that lock pnuematically. The locks are strong enough for the pods to not move while routing. A few months ago I was doing a test cut with what I thought was an 1/8" x 1/2" long tool, but in reality it was a left handed, 1/2" x 1-1/2" tool. Long enough to reach through the board, and crash into the aluminum base of the pod, while spinning the wrong direction. A right handed tool would have cut into the aluminum an inch or so, then get stuck in there real good and break. But because the left handed bit wasn't cutting, it just pushed the pod along the rail, with about 100 lbs of force, until I could hit the button. The bit had a little aluminum stuck to the tip, but I was able to keep using it for awhile longer, since I don't normally use the tip section of it. So figure a solid carbide router bit good for about 100 lbs of force, if it's not spinning but you're still trying to cut with it.

[sploo]

I really need to get my machine done so I can have some real world numbers to back me up. Just to make sure that using 10HP routers all day isn't skewing my view of reality.

It is! Some of the feed speeds you've mentioned you're running at work terrify me!

[sdantonio]

It is! Some of the feed speeds you've mentioned you're running at work terrify me!

If you read through Joe's thread on his machine he is routinely running about 70ipm, some of the people who have build "Joe Machines" with multiple start screws are running twice as high or higher.

[sploo]

The K2 I'm using is quite happy cutting 1/4" deep with a 1/4" bit at 120ipm, but I seem to recall Gerry mentioning deep passes with 1/2" wide bits at 400ipm!

Still, I'm sure the gear he's using costs a little bit more than mine...

[Zumba]

Cutting force doesn't really put that much strain on ballscrews. It's the linear motion guides that take the strain due to the moment forces. Imagine cutting a dado with a handheld router. If you put all your weight into the cut, you'd probably blast through the wood pretty quickly, and the actual cutting force would only be a fraction of your body weight.

The ballscrew experiences the most strain when the machine changes direction, because that's when the acceleration/g-forces are applied. A medium-duty machine with a 500lb gantry accelerating at 1G will put 500 lbs + frictional force on the ballscrew system. That's a lot more than the cutting force.

On most DIY routing machines, the gantries aren't nearly that heavy, so the ballscrews will likely last forever.