I recently bought a new Porter Cable 7518 router with variable speed control. It has five fixed speeds: 10,000, 13,000, 16,000, 19,000, and 21,000 rpm. The instructions indicate that lower speeds should be used with larger diameter bits, and that higher speeds may be used with smaller diameter bits. I am curious if there are other factors to consider. For example, in doing half blind dovetails for drawers with a hardwood (oak) front and pine sides, on a dovetail jig, should I use a higher speed on the oak and a lower speed on the pine, or vice versa? And what speeds among the five should I use?
I welcome any advice on setting speeds generally as well as on my specific question.
Thank you.
Replies
The bit diameter is the more important consideration. The wider the bit the higher the rpm will be on its tips versus the spindle rpm. Feed rate and wood type would be secondary. Woods having more resin or sap can burn with higher rpm and slow feed rate. Personally for your half blinds I’d start at 1600 and see how that goes.
You must have meant that the larger diameter will have greater speed at a given rpm than a smaller diameter bit. Therefore the larger diameter bit will require less rpm to cut at the same feed rate and will be safer.
Yeah, bit diameter is important, wood species is not. For a dovetail or straight bit, half inch is so in diameter, use the highest speed. For a 3-1/2 inch diameter panel raising bit, use the slowest, at least to start.
Larger diameter bits have the most potential to go rogue but it's not just because of their higher speed at the circumference of their rotational circle. The farther the cutting bit is from the axis of the spindle, the greater will be the dire effects of a tipping or other mis-management of the router as its cutting. A small tip of the router will move the cutting edge of a large diameter bit much further from it's intended line than with a small diameter bit.
Most bit manufacturers warn that bits over a certain diameter should only be used with the router in a router table or otherwise strapped down, with the workpiece moved rather than the router. Even then, there is still scope for a user-wobble o' the paw and a subsequent vicious bite of the large bit at the workpiece.
All router speeds, from fast to slow, will still impart a lot of energy to a workpiece via a large diameter bit digging in because of a user hand wobble or jerk. The router speed choices are, as others have said, about avoiding the burning of the workpiece rather than an increased danger from dig-in. Any dig-in of a large bit at any typical router speed is going to mean woe - to the workpiece and possibly the router user.
Lataxe
There are plenty of these out there. Here's one:
This forum post is now archived. Commenting has been disabled