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Best way to route a half-pipe?

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Forum topic by JohnMcClure posted 08-15-2018 09:47 PM 502 views 0 times favorited 11 replies Add to Favorites Watch
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JohnMcClure

234 posts in 762 days


08-15-2018 09:47 PM

I need to route a round-bottomed groove (if that makes sense) down the length of a 2×4. The groove must be such that the 2×4 can have a 2” diameter pipe (actualy 1.875”) laid down the length of it. Thus, calling the groove a half-pipe.

I see piloted cove bits, but the bearing is in the way. And I’m not sure they’re available in the radius I need (1”, or, preferably, 15/16”).

I’ve solved similar problems using a straight bit and a series of passes, ending up with a trough that works but has square lines lengthwise… too tedious for this application…

Any suggestions?
Thanks!

-- I'd rather be a hammer than a nail


11 replies so far

View joey502's profile

joey502

544 posts in 1640 days


#1 posted 08-15-2018 10:03 PM

What you are looking for is a core box bit. 15/16” will be tough but others are available.

View joey502's profile

joey502

544 posts in 1640 days


#2 posted 08-15-2018 10:07 PM

Mlcs has a 2” diameter listed for $29.

View John Smith's profile

John Smith

1318 posts in 284 days


#3 posted 08-15-2018 11:52 PM

have you considered using the table saw with a cove jig ?
http://www.rockler.com/how-to/cutting-coves-table-saw

.

.

-- some people are like a Slinky - - - pretty much good for nothing. But still make you smile when you push them down a flight of stairs.

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JohnMcClure

234 posts in 762 days


#4 posted 08-15-2018 11:52 PM

Thanks! Core box… I used to know that one!

-- I'd rather be a hammer than a nail

View OSU55's profile

OSU55

1835 posts in 2111 days


#5 posted 08-16-2018 12:14 PM



have you considered using the table saw with a cove jig ?
http://www.rockler.com/how-to/cutting-coves-table-saw
- John Smith

5” radius too big – core box router bit is the winner

View smitdog's profile

smitdog

397 posts in 2227 days


#6 posted 08-16-2018 01:56 PM

You can change the cove radius on a table saw any way you want by changing depth of the blade and angle of attack. Matthias has a calculator (only in mm) here: https://woodgears.ca/cove/calculate.html

-- Jarrett - Mount Vernon, Ohio

View Kazooman's profile

Kazooman

1117 posts in 2074 days


#7 posted 08-16-2018 02:28 PM



You can change the cove radius on a table saw any way you want by changing depth of the blade and angle of attack. Matthias has a calculator (only in mm) here: https://woodgears.ca/cove/calculate.html

- smitdog

yep, and the real fun comes when you also tilt the saw blade. You get interesting asymmetric coves like the one on this jewelry box I built years ago from plans in Woodsmith.

View GR8HUNTER's profile

GR8HUNTER

4579 posts in 834 days


#8 posted 08-16-2018 02:47 PM

you dont need TO BUY A jig just clamp a board to table saw just LIKE THIS :<))

-- Tony---- Reinholds,Pa.------ REMEMBER TO ALWAYS HAVE FUN

View Lazyman's profile

Lazyman

2399 posts in 1509 days


#9 posted 08-16-2018 02:55 PM

Just realize that using a table saw to cut coves yields a hyperbola (or is it a parabola) not a simple circular arc unless you run the board across the blade at a right angle. Router with core box bit is the best option, IMO, if you want a pipe to sit nicely into it.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View JohnMcClure's profile

JohnMcClure

234 posts in 762 days


#10 posted 08-16-2018 04:16 PM

Thanks everyone. I’ll buy a core-box bit now.
Good to know about the tablesaw, though, for times the RT isn’t up to the task; but I believe the RT is the right tool for this particular job.

-- I'd rather be a hammer than a nail

View fred43's profile

fred43

3 posts in 39 days


#11 posted 08-18-2018 06:49 AM

I agree with Joey502. The mlcs 2” core box router bit #8726 should provide the best circular cove results. As Lazyman pointed out, tablesaw coves are not simple circular arcs, but rather more hyperbolic or parabolic, i.e., more “V”-shaped than round. The curves are actually perfectly elliptical (except for minor deviations caused by the saw blade thickness). Tilting the blade relative to the table surface makes the curve asymmetric, as Kazooman pointed out, but it is still elliptical, just a different segment of the ellipse. Good luck with your “half pipe” cove.

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