Best Tool for Cutting an Ellipse in 4X?
I ordered the materials for my portico today. It’s time to figure out how I’m going to cut a curve in some 4×8 fir stock for corbells. I’m trying for very accurate carpentry here.
My choices are:
1) Saber Saw — I’ve got an older Craftsman saw. Are there blades available for 3.5 inch cut depth? I’m concerned about keeping the cut vertical.
2) Sawzall — Newer 3/4″ stroke Milwaukee. Is this controllable enough to produce an accurate, vertical cut?
3) Router — I’ve never seen an elliptical guide. But I could use a pattern cutter if I take the time to make a pattern with #1 (call this option 3a). I could also make a “true arc” elliptical jig with two pieces of 1X fastened together at an angle — guide it against two nails, one at each of the foci, and then finish the cut depth with a pattern bit (call this option 3b).
4) Bandsaw — I don’t have a bandsaw so this obvious answer is what I’m trying to avoid. I’m pretty sure this would be the right tool for the job but since I only have two cuts to make I can’t justify buying one. Are rentals available?
How would you do this?
Replies
A high quality jigsaw, bosch or festool, will do it just fine. An old craftsman jigsaw won't give you a square cut, trust me, I've tried it. There are blades available up to 6 or 7 inches long, but for what you're looking for, it shouldn't be hard to find something at lowes or on amazon.
zak
"so it goes"
I've never done this, but I just saw a trick in FHB's book "Tricks of the Trade" (1994; the best of the tips & techniques column in the magazine) page 49, sent in by Jeff Morse. He says a rolling bandsaw is the best way, but there is a trick to using a sawzall:
It takes 2 people: one to run the saw, and the other to use an adjustable wrench to guide the blade on the other side of the board. You can see the picture in the book if you can find it.
I would not use a jigsaw as the blade would flex.
erikpeter
Good luck trying for accuracy with a jigsaw in 4X...ain't gonna happen.
I'd go bandsaw, but I have one so it's an easy decision for me. Even with a bandsaw, though, I'd be inclined to make an MDF template of the curve and use a router with my big pattern router bit. 2.5" of cutting edge on a 3/4" diameter straight bit. After eating the first 2.5" of the 4x, I'd remove the template and use the work piece as it's own guide.
obvious answer
That is true in more than one way - as good as an excuse as any to buy a new tool!!!!
A good skip tooth blade will give quick and accurate complex cut in 4x material, did a number of 4x6 for own house easily with a low cost Taiwan Delta reproduction bandsaw.
I once had the same dilemna. Solved it by going with the following design, tangential cuts done with a skilsaw (circular saw) from either side, finished with a sawzall and cleaned up with a belt sander.
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"he...never charged nothing for his preaching, and it was worth it, too" - Mark Twain
Make a template and lay out your ellipses on the 4×8's. Rough cut with a chain saw, finish with a sander.Joe Bartok
Thanks Guys, I appreciate your ideas.
My Dad has a nice Bosch router. I'll think about borrowing it and practicing on some scrap wood to see if I can keep a vertical cut. I'm probably biased against jigsaws being able to keep vertical cuts because of my experience with my cheap Craftsman saw. But if I enter the cut at a right angle to the piece, maybe I can turn the cut and keep it vertical once I'm in the piece. I'll try, but I'm skeptical.
I don't understand the trick with using an adjustable wrench to guide the blade of a sawzall. Are you talking about loosely pinching the blade from the back with a crescent wrench or something? So I'd need to put two curves on the piece and get them perfectly aligned so the second guy can follow the curve on the back side? This sounds too scary if I'm understanding it right.
The template + router approach was what I was leaning toward before posting. I'll need to see what kind of cut depth I can get for doing subsequent cuts (using the first cut as a guide). My router is also a cheap Craftsman model that I've had for about 30 years!
Re buying a bandsaw, I'm always up for an excuse to buy a tool. But my game is to make sure I can pay for it with sweat in the forseeable future. I can only see two cuts I'll need to use a bandsaw for so this is tough to justify. Plus, bandsaws are huge and I don't think Mrs. Powpowhound would appreciate me storing it in the living room. But it's probably worth seeing if I can use a friend's bandsaw if logistics allow it.
Tangential cuts with a circular saw is probably what I'd do if I was cutting an outside curve. But this is an inside curve. Good idea though. A variation on the theme would be to cut a series of kerfs to the curve and then breaking them away. But I think that would take a lot of sanding to get all the blade marks out.
Chainsaw -- I love it. I'm just not skilled enough with my chainsaw to get super close, but I could definitely see using my chainsaw for making a rough cut to reduce router cut depth.
It sounds like a bunch of ways to skin the cat. The other way I was thinking involved a router:
Make a jig that has two straight sides that meet at an angle. For my application it would need to be an obtuse (greater than 90 degree) angle to produce a shallow cut. I could do this with a piece of plywood or a couple of 1 X 4s lap jointed together to make the corner. Drill a hole near the corner for my router blade to stick through and bolt the router to the jig. Sink two lag bolts into the top of a piece of 4X scrap -- these represent the foci of the ellipse. To produce a symmetrical ellipse in the workpiece, you'd make sure the bolts are the same distance from the edge. Clamp the workpiece to the scrap 4X with a couple of 2X spacers in between. Then to cut, guide the jig so that both straight sides of the jig are always pushed against the lag bolts.
It would take a little bit of fiddling around to find the best angle and lag bolt spacing. It think it also wouldn't produce a true ellipse because of the constant angle, but it would probably be a pretty good imitation of one.
Has anybody heard of a jig like this? It is reportedly an old boatbuilder's trick to produce a fair arc. Classically, I think you'd position the bolts and straight edges so you'd be pushing back against them. But I think it would be safer for the workpiece if you were pushing into the workpiece -- that way you could never cut too deep even if you wandered off the bolts.
I bought my Festool Trion jigsaw for work similar to what you want to do.
Don't listen to the nay-sayers; it WILL cut square in thick stock with the right blade.
It's a bit pricey at about $260, but it's worth every penny when it makes the job easier.
Woo-hoo! A reason to buy another tool!I'll audition my Dad's Bosch before I take the plunge on a better jigsaw. But this has an advantage in being very straightforward.Do you need to enter at close to 90 degrees to keep the blade straight?
The Bosch is good, and a heck of a lot better than that Sears. It's the jigsaw I had before I bought the Trion.
You should be able to get real close with it, and have to do some hand work to finish.
But the Festool really works. They make a longer,thicker, stiffer blade for deep cuts, and with the blade guides set close, it will make the cut with a minimum of drift. And I do mean minimum.
And you don't have to enter at 90 deg. Just start cutting slowly until the blade is fully engaged .
I agree with shep the Festool jigsaw will cut 4ins square it is expensive, in Australia we pay over $500Ad I have been using one for the last year if you buy one you will not regret it .You can make it fool proof but not idiot proof
I've the festool and I'd have to say you would be hard pressed to be able to keep the blade square through curves and 4 by stock
They are fairly mild curves and would probably need some cleaning up but it is the only jigsaw that will come close to doing the jobYou can make it fool proof but not idiot proof
I've done curves like this with a router and template in 3" stock but not 4". I believe I've got a 1/2" bit with a cutting length of 3". I used a 3/4" O.D. guide bushing so the template has to be 1/8" undersized if the actual dimension of the curve is critical.
Take your time making the template and make sure you keep the stock well supported with maybe supports on the sides for the router base to ride on as well.
It's worth it to hog out most of the wood up to your cutting line with a sawzall, jig saw, or Lancelot tool, so that your router doesn't have to work so hard.
Take multiple passes down to the maximum depth of your cutting length. BE careful, go slowly under control, then maybe get rid of the template and bushing, and use the shank of the bit to follow the wall of the curve you've just cut. I'd slow the router speed as you get more length of bit exposed. I don't think you want to be cranking at 20K with 4" of bit below the base of the router. BE careful, wear eye and body protection.
You can do it.
Try this. Watch the video. Jim is the master.
http://www.miterclamp.com/Woodworking_video_index.htm
I don't know if anyone will read this, but I'll do a quick reply with what I ended up doing.I watched the videos posted by mike585. Later I found that the current issue of FHB (June '06?) has a section on making elipses toward the end of it.I made a trammel jig that I thought was beefy enough to mount my router on. I did a bunch of test passes but felt the thing was just too prone to wandering off the path to run my router on it. I had the MDF screwed together and to a stable surface, but it's easy for the short axis bearing to come off the guide surface. And I didn't think I had the physical skill to properly run a router on it.So I used the trammel to draw an ellipse on MDF. Then I cut the pattern using my jig saw and sanded it smooth. Then I clamped the pattern to a piece of 4 X 8 and drew an outline of the corbel I needed to cut. I took the pattern off the 4X8 and used my new Bosch jigsaw to cut about 1/8 inch outside the line. It is hard to find blades long enough but I finally found some that will go all the way through the 4X on the downstroke. The Bosch saw (the new one with blade stabilizer) does not keep a perfectly square cut, so it was important to cut a bit off the line.Then I clamped the pattern onto the workpiece and used a 1/2 inch X 1 inch pattern bit to route along the edge of the pattern. If the pattern moves, you need better and/or more clamps. Then I took the pattern off and lowered the bit as far as I could, leaving about 5/8 inch of shaft in the collet. Then I flipped the 4x8 over and mounted a 1/2 inch bit with a half inch bearing on the bottom. Unfortunately, the combined lengths of the bits is not quite long enough to get through 4X material -- I checked every bit carried by HD and Lowes and three local lumber yards and couldn't find appropriate router bits. I think it's a conspiracy. Anyway, I alternated using a 1/4 inch roundover bit to make room at the upper edge with running the bottom-bearing bit and finally made it all the way through with only a thin ridge of material in the middle of the 4X corresponding to the gap between bearing and cutter. If I had to do it again, I'd look harder for either a longer top-bearing half-inch pattern bit or a longer bottom bearing bit to avoid all the fiddly work to avoid burning the top edge of the wood with the shaft.I sanded with 60-grit sandpaper loaded in my random orbit sander. I stopped there for the evening. Tomorrow, I'll work down to 220 grit. It looks beautiful. Anyway, I thought I'd post what I did in case anybody does a search and needs to do the same thing. It was a lot of work with all the fiddly edge rounding/pattern cutting/edge rounding/pattern cutting... But the result was worth it. Thanks to everyone who responded to my question.
Thanks for the follow up. All too often here we're left wondering how things turned out.
-- J.S.
Glad everything worked out.
Now we need to see some pictures!
Two options seem to make sense.
If transportation and a bandsaw are available, take the pieces to the band saw.
If that's more work than the router option, go with the router. Rough it and start with a template and top bearing bit. Then use the finished surface to guide that same bit farther down. When you get more than half way, flip the workpiece and continue with a bottom bearing bit. Use a block of the material you cut off in the roughing step to support the outboard side of the router to keep it from tipping.
-- J.S.
Make the template accurately first. With a number of passes and a top bearing bit you can get more than halfway thru. Remove the template, turn the work piece upside down, use a bottom bearing bit to follow what you already cut.
mike
Do you have a planing mill or wood shop in your town? Pay them a visit - 2 cuts on their bandsaw won't take long.
See Mike4244s answer...it's the correct one....unless you have a bandsaw and a spindle sander handy....
Powpowhound,
I've done the jig saw trick but you have to have a good one and cut away from the line so you can clean it up with a sander.
If your beams are easy to handle I would use a bandsaw and again leave room to clean up with a sander.
The Hot Ticket though is a hand held portable band saw! We can cut any design up to 10" thick material. We did an entire house roof eve in 4x12 applied tails with a scroll design. Used it on Trellis beams and interior detail beams. The down fall it's a $1500.00 tool! But well worth the cost and time savings for us, it more than paid for it's self.
Wouldn't be worth it for one small job, but it's sure a nice tool!
Howie
"Work smarter, not harder"...and we've all grown just a little "spoiled" with modern tools and technology, sometimes.
Get yourself an old-fashioned bow saw with a narrow blade, and go to it! Lay out your lines on both (opposite) faces, and just take your time (and you'll need it, lest you work your arm right out of your shoulder!)...A few strokes at a time, and you'll be able to stay close enough to your guidelines (keep checking) that a little touch-up with some sandpaper will probably be all that's necessary.
After all, when corbels were first developed, they cut 'em out of stone, so don't complain too much about a little actual physical effort! <grin!>
Thank you all.
I found a Milwaukee portable bandsaw at Loews. $300 with case and blade. It's got a 4.5 inch capacity (thickness). I'm not sure what the lateral capacity is, but you can always nibble away, can't you. Half-inch blade. And I could store it with my other tools rather than in the living room!
Has anybody ever used one of these for an application like this? My impression was that these are usually used to cut pipes. But if they work for wood and can keep a square cut, it seems like it would be great for not only these two cuts, but also for notches, birds-mouths, etc.
By the way, if you have the patience for the download, the videos that Mike585 posted are excellent. Jim is not only the master. He's hilarious too. I'll use his technique to draw the ellipse.
I also just went and got a bottom-guide half inch router bit to complement my top-guide half inch pattern bit like you guys suggested. I'll need it for some box joints and bolt access holes, whether or not I use the router for the ellipse. So thanks for the idea about flipping the piece over and using the existing cut as the guide.
I agree with Strawboss except use a spoke shave instead of sanding to clean it up. And if you don't have a bowsaw then sharpen an axe and stand the beam up and start chopping.If it's a portable bandsaw for cutting corbels that you want then this is the puppy to buy.http://www.falbergsawco.com/