Wood project - sawing round pieces out of plywood (Hammer?)

[baileyuph]

My business got a set of patio chairs in for redo, everything upholstery and the round wood frames in the chair bottoms and backs.

I saw wood, but sawing a round piece, lets say near perfect doesn't come up often.  These round seat bottoms and seat backs will be upholstered and such but have to be near perfect for they are attached inside round metal frames.

At my disposal is sabre saw and band, also router. 

Anyone done this and have a point or to?  Or is drawing the cutting line (a circle) on the wood and just going real slow about as good as it gets without some kind of a jig (in my mind a jig that allows the wood to spin perfectly while sawing of a band saw, would be less tedious).  I don't have that jig and for the few I cut, well like I said, just pattern and go slow on the band saw?

It isn't a heavy production issue.

Doyle

[sofadoc]

........ some kind of a jig (in my mind a jig that allows the wood to spin perfectly while sawing of a band saw, would be less tedious).

That's basically how I do it. I butt my bandsaw up next to a wood table, drive a nail at the desired spot to spin on while cutting.

A lot of those patio frames aren't consistent. I've cut wood pieces before that fit perfectly in ONE of the frames, but not the others.

[gene]

I do not have a band saw, only a jig saw. I can cut circles with the jig saw quite well if I go slow. I don't cut a lot of them so going slow is not that big of a deal.

Don't forget wood expands so don't make them super tight if they sit down into a recess in the chair.

gene

[byhammerandhand]

Sofadoc has a standard way of doing it.

When I've made round tables, I screw a piece of plywood or Masonite as a replacement sub-base on my router.  On the unseen side, run a screw into a pivot point.   Plunge the router in and run it around the ring, plunge a bit deeper and repeat until you are through.   If that sounds too treacherous, cut a little oversize with the jigsaw or band saw and trim to the line with the router.   

Plywood will be more stable than solid wood when the humidity changes.  But if you have to use solid wood remember that wood changes hardly at all in length (with the grain) and more tangentially and radially to the annual rings.

The other way I do it is to draw the circle, and saw roughly to it with a band saw or jig saw, then use a disk sander to trim and fit.

........ some kind of a jig (in my mind a jig that allows the wood to spin perfectly while sawing of a band saw, would be less tedious).

That's basically how I do it. I butt my bandsaw up next to a wood table, drive a nail at the desired spot to spin on while cutting.

A lot of those patio frames aren't consistent. I've cut wood pieces before that fit perfectly in ONE of the frames, but not the others.

[baileyuph]

The project requires 4 round pieces, 2 at 15 inch diameter and 2 at 10 inch diameter, as I recall.  The dimensions are at the business.

You guys are encouraging, offering two or three different ways.

That router technique, scribing a deep cut in a work surface and then laying the piece to be cut on it and route through it.  Did I understand you Hammer?  Slick!  If I had a trammel or ?  I could set that up with my 2 hp router.  

If I cut it with a jig or a band, then set up the disc sander on my shop smith, the inference on sanding is spin the cut piece to sand, do I understand correctly?  If the sanding is just a matter of manually rotating the rough cut circle piece  while sanding with the disc, that could be tested.  I have a large disc sander for the Shop Smith.

Clarifying Dennis bandsaw technique:  obviously the pin or center of rotation is at the desired radius.  At the start of cutting, what do you do to facilitate the cutting start, just cut away enough wood to get the band saw blade to the start cutting line?

BTW, these chairs are right on, same dimensions that is.  I am going to undersize the circle cuts about one 1/16 on the radius, that would generate about 1/8 clearance for the upholstery material to be stapled on the edge.  The thickness of the vinyl will probably drive this.

Could be a fun project, enables me to polish old skills.  

A trammel with the plunge router would be pretty accuacte, wouldn't it?

Hey!  What about using some plastic composition wood rather than plywood?  Hope you know what I mean.  This is for patio but it has a cover.

There is a proper name for the plastic composition wood I am visualizing.  As long as one can staple into it and I would think so.  Is mellomine what I am trying to think of?  Something to check at the lumber store.

You got me thinking,  thanks.

Doyle

[sofadoc]

Clarifying Dennis bandsaw technique..............  At the start of cutting, what do you do to facilitate the cutting start, just cut away enough wood to get the band saw blade to the start cutting line?

Yes.

[byhammerandhand]

Here are a couple of photos.   Excuse the dust as I had to dig this out of my "Pile o' Jigs"

First shows how the router mounts to the fancy jig.   Remove the plastic sub-base from the router and mount onto the plywood jig.



Further out are holes for pivot points for various radii.   If both sides are show wood, you can put a roofing nail into a square of Masonite, then mount the Masonite with double-sided carpet tape.   Heat the tape with a hair dryer to get it to release.

[byhammerandhand]

The Shopsmith* is a perfect tool for this.   You can make a plate that fits in the table's miter slots, set your pivot point and use the quill to extend the sanding disk closer and closer to the line.   If it's too big, put it back on the pivot and sand off a bit more.

The project requires 4 round pieces, 2 at 15 inch diameter and 2 at 10 inch diameter, as I recall.  The dimensions are at the business.

...

If I cut it with a jig or a band, then set up the disc sander on my shop smith, the inference on sanding is spin the cut piece to sand, do I understand correctly?  If the sanding is just a matter of manually rotating the rough cut circle piece  while sanding with the disc, that could be tested.  I have a large disc sander for the Shop Smith.


...
Doyle

* The table saw mode, IMO, is SS's weakest point.   All the other accessories really do work well together.   Such as using the lathe center and horizontal borer to drill into the center of a spindle.

[kodydog]

The other way I do it is to draw the circle, and saw roughly to it with a band saw or jig saw, then use a disk sander to trim and fit.

That's how I was taught to do it. This method will work well if the circles are not perfect and you need to make separate templates for each chair.

[baileyuph]

You guys have provided great information.

I am going to try most of your techniques for the experience of it all.

First I cut the pieces (or a piece) with the band saw.  Worked.  With my band saw, the process encouraged a go slow and keep the process in control.  

Then, I tested the saber saw.  I was surprised, it went fine and the process was easier to control, compared to the band saw.  I have a Dewalt saber, a commercial grade with plenty of power and without changing the blade to new, it really went through the three quarter ply wood very strongly.  I don't think it would have been the same experience with my much older light weight cheap saber saw.  

BTW, is the jig the same as the saber saw?  I have both by those titles and I call the portable saber or sabre saw a saber saw.  LOL.

The jig, my other saw, is a recriprocal blade mounted in a frame with a small table, in a word much smaller than a band saw (I did not nor plan to test cutting with that saw).

Ok, are you ready for this, I want to try the router, plunge router next and I can sense already it will carry (potentially) a bit more accuracy.  It might be the preferred ticket, especially when that level of accuracy is required.

Wood working has been a side line of mine, but it covers so much diversification.  Maybe in furniture work it is considered cabinet making?

Wood working is in many respects like upholstery, you can engage at so many levels.

Try to keep you guys posted, busy at the shop therefore; might be a couple days getting back to this.  Already, I can see that the quality of the tool as well as the technique of using the tool plays out into whether it is the desired tool or technique.  Confusing?  LOL.

Doyle

[byhammerandhand]

This came across my screen this morning and seems to explain it much better than I did:

http://www.woodworkingtips.com/etips/etip030201wb.html

[baileyuph]

Super clear!

One point that comes to mind is on very small circles, something of a radius less than that of the router base, would be the approximate limit.

It won't on a circle of 5 to 6 inch radius, which is one of mine.

Never stop learning do we.

Probably what I will learn also is, to make two passes with 3/4 plywood.  two or maybe three?  That will be tested.  An underlayment under the stock being cut will be needed.

It will be interesting to see how the router reacts as it closes in on cutting the cicle.  A preparatory step would be to insure the trammel pin is anchored not only through the stock being cut but also into the underlayment (underlayment meaning protection layer to keep the cutting bit from damaging a work surface.

Thanks

Doyle

[Mojo]

I do it like Keith. I use a compass to get my perfect circle line drawn and then cut it out with a jig saw. Any uneven spots I clean up with my belt/disc sanding machine.

Chris

[byhammerandhand]

I think it would work, just that the pivot pin would be under the router and not outboard.

Your backer-board ("underlayment") is something you can secure to your good piece with double-sided carpet tape.   I like to use the "outdoor" type as it's stronger stick.  Unless you don't care if there is a through hole in your piece.

One point that comes to mind is on very small circles, something of a radius less than that of the router base, would be the approximate limit.

It won't on a circle of 5 to 6 inch radius, which is one of mine.


Thanks

Doyle

[baileyuph]

I understand on that small trammel radius, my mind got tangled with the possibility that if the circle becomes small enough, might do it with a hole saw, if it is available in the size desired. 

The carpet tape idea, I see how that would work to keep things stable.

Trying to finish an eight way tied spring job on a settee, then back to this trammel concept.

Doyle