How to make tapered end of round groove. HELP!

[Jaze Derr]

I am trying to replicate the wooden arm that goes on an old metal patio chair. I can't figure out how to make the groove that the pipe arm fits into. See pictures. I have a 3/4 core box bit that seems to be the best fit. I have tried a couple different ramps and such, but I can't seem to get the tapered end looking right. Also, I haven't been able to keep the router perfectly straight, even with an edge guide.

Suggestions? Other ways of doing this besides a router? Would it be possible to do this on a router table, so I can use the fence for guidance?

This is for a friend, for his wife's birthday, so I'm up against a deadline in the next week or so.

Picture of the original, and one of the blanks I have ready for grooving:
https://i.imgur.com/C9QI3HTh.jpg

the easy end:
https://i.imgur.com/orow7kvh.jpg

the tapered end:
https://i.imgur.com/Tx0n1TEh.jpg
the groove is flat for the first 6", then rises a total of 0.42 inches from that point until the end of the taper. I've tried making a ramp from those numbers, but the taper is way too long. How do I figure out what slope of ramp and where to start it?

I'm so lost and frustrated right now. I'm willing to do it by hand, but I don't have any carving tools, other than normal chisels.

[Mike Kreinhop]

The solution for this screams "router table" to me. Assuming you can find the correct cutter, I would make a series of passes through the table starting with the shallowest cut first at the open end and stopping short of the closed end. Then I would raise the cutter slightly for the next pass and stop farther from the closed end. You might have to finish the closed end by hand to remove any step marks from the router cutter.

I'm also thinking of a more complicated method that uses a platform on the router table and wedge under the closed end of the piece to lower it onto the cutter head as it's passed along the fence to create the uniform transition to the final depth.

[phil harold]

I wood do it with a ramp
The ramp I make is usually curved to extract the bit faster at the end

If you do it by hand, sandpaper and a rasp should get you what you want

ramp explained...
http://world-of-wood.blogspot.com/2012/02/routing-stopped-flutes.html

[Charles Lent]

I would also do it with a curved ramp to tilt the router as it reached the end of the cut. Some experimenting will be necessary, but the end result should be very repeatable.

Charley

[glenn bradley]

I would also use the router table. Layout a mark on the fence at the location where yo would start to lift the piece off as you slow the feed to a stop, lifting the material completely away.

[Wayne Lomman]

This type of finish to a groove is done on a spindle moulde/shaper. The cutter is about 150 diameter. The piece is machined with one edge on the table and the grooved face against the fence. Routers have difficulty replicating this effect. Do what you can with a router and hand carve the last bit if a moulder is not available. Cheers

[Bill Dufour]

I agree use a shaper and a large diameter cutter.
Bill D.

[John Patric]

Could be done on the TS, as in cutting coves on a TS, for the bulk of it, the tapered end could be fashioned using some hand tools.

[Peter Christensen]

Take a compass and some stiff paper and draw some circles of differing diameters. Cut them out with scissors to make radius gauges and check the end of the groove. Alternately try the saw blades you have including the ones from your skilsaw, paint can and plastic lids. Take a saw blade close to that diameter and make a stop cut. Take the piece and put it on the router table and with a round nose bit cut the straight section of the groove. Finish the remainder with a gouge, rotary file, mini sanding drum and sanding paper. You should cut the groove in a larger piece of wood first and then cut to length and shape the outside after the groove is done. Safer and easier to clamp that way.

[Yonak Hawkins]

Jaze, I have some ideas but first I'd like to verify that I understand the cut you want to make. This drawing is a side view cut-away of the groove you'd like to make. Did I get it right ?

388528

[Peter Christensen]

Yonak your drawing is incorrect. Picture a buried saw blade cut that’s stopped before going through the end. Straight with an arc of the radius if the blade at the end.

[Yonak Hawkins]

You mean like this ? Is the end radius the same as the cove radius ?

388529

[Peter Christensen]

No. End radius is from a shaper cutter as mentioned by another before my posts. It will be the size of the bent chair frame tube it will fit. 4”+.

[Jim Becker]

If absolutely necessary, the tapered end could also be done manually using a very sharp carving gouge of appropriate width. Do the majority of the slot on the router table with feather boards and stops to keep it spot-on and the finesse the end with the gouge.

Or...if you feel like buying a new tool... :D :D :D ..invest in a CNC.

[Yonak Hawkins]

I believe I have a solution using a router table if I can get some dimensions and confirmation of the general profile.

[William Young]

I have to ask if it really matters if the groove ends in a true taper. Why not use your router and core box bit, or better, router table and cut the groove stopping it just short of the end of the arm. Wouldn't that work just as well ?

[Tom Bender]

Before you spend time trimming to width and shaping the top, cut the groove. It's easier to work with an oversized piece.

[Mike Berrevoets]

I’m assuming the groove tapers up just so,it isn’t seen on the end. If that is true (and it is being painted) then I’d be tempted to just route the grove through and then glue in a short piece of mating dowel on the end then trim to fit and paint.

[michael langman]

What is the total length of the piece? Maybe I can figure out the correct angle of the slope and the starting pint.

[Cary Falk]

I have to ask if it really matters if the groove ends in a true taper. Why not use your router and core box bit, or better, router table and cut the groove stopping it just short of the end of the arm. Wouldn't that work just as well ?

Unless I am misunderstanding the situation this is my thoughts as well.

[Curt Harms]

Could be done on the TS, as in cutting coves on a TS, for the bulk of it, the tapered end could be fashioned using some hand tools.

A table saw with molding head will create that effect, sort of like the large diameter shaper cutter. The only new source I'm aware of is Corob Cutters, I don't know that the Craftsman head is still sold. Corob sells a 1/2" & 3/4" flute molding knives if those will work.

[Dave Richards]

Are you going into production making these armrest pieces? You only need to make two of these things at most, right? And you have a short deadline. Use the core box bit and get it close. Then finish the shaping by hand. It'll be close enough and it's on the underside where it won't be seen when it is installed. Even if you run the core box bit slightly long, it won't matter. Just don't come out the end. Do you have the chair in your shop so you can try the fit?