Newbie wants to climb-cut table top

[Bob McCoy]

My first project is a round table top. I have researched the group's past postings on direction of cut with a router, but still am not sure for my situation. I would appreciate some knowledgeable help.

Table diameter after cutting will be 46 inches. The table rim is mahogany, approx. 1.75 inches thick; the mahogany is glued and splined in a hexagon shape from pieces that are about 5 inches wide. The grain on each piece is fairly straight. I have made a 2 by 6 stretcher that forms a diameter inside the hexagon, and have a 0.25 inch carriage bolt protruding from the center of the stretcher for my pivot. My router is restrained by two 0.375 inch-diameter steel rods through the router base to the pivot. The bit is a

0.5 inch diameter, with two straight flutes.

I would like to climb-cut to minimize tearout. I believe the trammel is strong enough to keep the router in check. However, the bit with be partially exposed (about a quarter inch) as I hit the mid-point of each of the hexagon's sides. Will this cause any problems? I know to make multiple passes, increasing depth each time, but I'm not sure of the effect of the bit coming partially out on each side.

Thanks for your help.

Bob

[Mike G]

By increasing the cutting depth in increments climb cutting isn't necessary to avoid tear out and does the job with far less chance of the router running away from you.

[Ehvee8or]

Apparently I'm an even greater newbie than the OP. What's a climb cut and why would I want to use one?

Thanx

[Andy Dingley]

Dangerous, and you wouldn't want to.

Replace the wheels of your car with big sawblades and drive along. That's a climb cut. As you might imagine, there's quite a force generated to drive the saw along relative to the road/workpiece.

It's safer to feed the other way. The workpiece is pushed back at you, and you both oppose this and feed it by pushing in the same direction. Things are under control.

Climb cutting is hazardous, because you're either pushing the feed in one direction or restraining it from leaping ahead of you. As you feed, and as the cut changes, then the force you need to apply changes direction. This is always somewhat hazardous.

Climb cutting is really only done (for hand tools and woodworking) with routers and small cutters. For saws and planers, it's just far too hazardous. No-one likes doing it, but it can reduce break-out when working across the grain, especially when you reach the end of a cross-grain edge.

-- Die Gotterspammerung - Junkmail of the Gods

[George M. Kazaka]

[CW]

I haven't seen a hand held router yet that would run backwards.

[John Thompson]

FWIW, in the metal trades, running a mill cutter in climb cut gives the smoother finish. Of course, everything is very securely clamped down. Dunno about this in WW.

John

[CW]

Climb cutting is more efficient for cutting any material. machine rigidity and fixturing are often a limitation though.

[Erik Ahrens]

I wonder if a spiral up or down cut bit might be better than straight flutes?

Erik

[Erik Ahrens]

How about using a spiral up cut bit instead of the 2-flute. It tends to pull it self downwards (I think). Or is it the down cut spiral?

Erik

[CW]

Won't help. Think about it.

[Erik Ahrens]

CW, thinking about it is how I came up with the suggestion. Considering I've had my router for two months, I thought I was contributing an idea no one else brought up. If you would be so kind as to elaborate on the 'think about it', I would be most grateful for the wisdom and advise. I don't want to wear my router anytime soon 8~).

Regards, Erik

[CW]

The problem with climb cutting is that you are cutting in the same direction as the cutter is trying to pull the router. Holding the router back against its urge to jump forward is tricky and not recommended in most cases. The spiral bits ill help from a finish standpoint but will be the same as strait bits in their propensity to pull the router forward. That said, climb cutting is considerably more efficient. Smoother cuts with virtually no tendency to tear out, better chip ejection and far better cutter life result. Unfortunately, for the majority of routing, climb cutting is only practical on machines (such as CNC routers) that have backlash control.