Advice requested on stopped grooves

[knimac]

I want to make stopped grooves in 3/4" wide rails that are 1/4" wide and 1/2" deep. I assume router table is best choice, "plunging" piece onto/into bit and lifting off/out when cut is finished. My question is whether to use 1/4" straight cutting bit and drop the rail onto the table, or use rabbiting bit or slot cutting bit and push the rail into the fence. On the assumption you can understand my poor description, is one method better/safer than the other? If into the fence is best, is one of the two bits I mentioned preferrable? Thanks for your consideration.

[jarhead]

Just a thought

Why not "sandwich" your 3/4" wide stock between 2 pieces of plywood to provide the support for the router and route the stopped dado.

http://www.newwoodworker.com/stopdado.html

[Tom Miller]

I can't think why one or the other would be better/worse. But, there are other things you can do to make either approach safer. E.g., if the 3/4" pieces are not already cut to size, you could make multiple grooves, and then rip to separate after.

Regards,
Tom

[RayintheUK]

On the assumption you can understand my poor description, is one method better/safer than the other?

Your description is spot-on, knimac! The answer depends upon how much lateral freedom you'll need or have at the extreme ends of the stopped grooves.

If you plunge downward onto a 1/4" straight bit, then you'll have a slight bow at the entry end, due to the stock coming down in a slight arc.

If you were to push the stock forward onto a slot cutter or rebating bit, then the arc would be the radius of the bit size.

I would plunge vertically downwards, but I wouldn't attempt to take out all the material in one pass with a 1/4" bit. Mark the fence with the leading and trailing edges of the straight bit, anchor the right-hand end firmly, ease it downwards onto the bit, push to the left until the trailing edge is in line with your layout, ease back to the right just a hair, then switch off the router. Remove the workpiece once the bit has stopped spinning.

You may well get away with lifting the stock from off a spinning bit, but beware that if you skew the workpiece even by a hair, your groove will be damaged and oversize and you could get the piece flung at you.

HTH

Ray.

[Stormbringer]

My question is whether to use 1/4" straight cutting bit and drop the rail onto the table,

knimac,

I don't think a straight bit would work since only the edges do the cutting (used to enter the workpiece from an edge of the workpiece.) Sounds like you want to "plunge cut".

Your method seems a little risk-A to me. Why not go from above with a plunge router and just clamp the same height stock to the left and right of your piece so you have more surface area to support your router with a stop at each end? I don't see how "Dropping the piece" onto the bit can ensure accurate repetitive starting points if you can't see the bit enter the workpiece. Or am I misunderstanding you...which is most likely the case these days.

Good luck,
Greg

EDIT: I see jarhead gave a similiar reply while I was typing. Sorry for the dup post.