An arc (or arch) cutting template

[sploo]

I've been building a version of Marc's Kitchen Helper (http://www.thewoodwhisperer.com/videos/ ... en-helper/) and was scratching my head on how best to create the arches in the horizontal sections.

I'd usually just throw something at the CNC machine (i.e. cheat) but it's out of action at the moment.

Marc's technique is to rough cut the curve on the bandsaw, then sand with a flexible sanding block, but I fancied trying something different.

My solution was to use an improvised circle cutting jig with a router, to cut suitable arcs for the two different lengths on sheets of 1/4" (6mm) MDF.

I then screwed 1/2" (12mm) blocks on the underside of the MDF to trap the material to be cut, and also glued on a piece of sandpaper to help resist movement.

A quick rough cut on the bandsaw to remove some waste material, then a trimming bit on the router table makes quick work of the pieces.

It took a little bit of time to make the templates, but machining the stock is then so fast (and with a good finish) that it's worth the time, even for this short production run. If I were making multiple copies it'd be a huge time saver.

On the subject of safety; note that the stock being cut is 3/4" (18mm) thick, so applying pressure on the top of the jig holds the stock against the sandpaper. If the blocks on the underside were also 3/4" it might risk movement of the stock (being pulled into the router bit) as it (the stock) wouldn't be held against the sandpaper with as much force.

 

[mseries]

I usually stick the template to the stock with double sided tape. Usually holds very well

 

[sploo]

I usually stick the template to the stock with double sided tape. Usually holds very well

I considered that, but my tape is old and gunky, and I didn't fancy cleaning the mess off the stock! The sandpaper and blocks on the underside worked surprisingly well.

 

[mouppe]

By chance, I have 36 arches to cut tomorrow. I used a slightly different method to make my template last time, but I'll be using your idea next time. My router jig was identical to yours but because my radius was much smaller, I had to route in both directions using a double-bearing flush trim bit to avoid massive tearout.

 

[mseries]

I usually stick the template to the stock with double sided tape. Usually holds very well

I considered that, but my tape is old and gunky, and I didn't fancy cleaning the mess off the stock! The sandpaper and blocks on the underside worked surprisingly well.

Yes it can be a chore to clean up if the tape doesn't pull off properly, then for half a dozen pieces ....or more ......; Anyway thanks for showing this

 

[Steve Maskery]

And just a tip for the bandsawing:

Make a notched single-point fence clamped to your normal fence, but up off the table so that the workpiece can pass underneath. Set the notch just to keep the template shy of the blade. The blade sits in the notch. As you saw, keep the template against the fence. You will end up with a workpiece which is just a mm or so too big and you can clean that up on the RT as you have done above.

 

[sploo]

And just a tip for the bandsawing:

Make a notched single-point fence clamped to your normal fence, but up off the table so that the workpiece can pass underneath. Set the notch just to keep the template shy of the blade. The blade sits in the notch. As you saw, keep the template against the fence. You will end up with a workpiece which is just a mm or so too big and you can clean that up on the RT as you have done above.

That's a nice idea. I've got a fairly wide blade on the bandsaw at the moment though, so I deliberated cut the waste with a series of mostly straight cuts as I don't like to force curve cuts on a blade I use for straight cutting (and I was too lazy to change to a thinner blade and adjust all the guides).

 

[Steve Maskery]

Well if you are doing it with a wide blade, just make a load of radial relief cuts first, to give you a bit more clearance for the back of the blade. It shouldn't be too much of a problem on a shallow curve like that.

 

[sploo]

Well if you are doing it with a wide blade, just make a load of radial relief cuts first, to give you a bit more clearance for the back of the blade. It shouldn't be too much of a problem on a shallow curve like that.

Yea, that's mostly what I did (though only a couple of relief cuts were required). TBH given the shallow arc and the fact it was pine I probably didn't really save myself any time using the bandsaw, and could've munched through it on the router table immediately - at the expense of a bit more dust.