Repeatability without TS?

[Phil Crow]

I need to cut about 50 strips of 3/4 birch plywood at EXACTLY the width of 2 of said strips at 24" long. I don't have a table saw. The straightedge that I have (one of the ones you get at the borg--aluminum, 2 piece, 97" total length) bows in the middle by about

3/32" on the 8' cut, quite a bit less on the 4' cut. This is because I apply gentle pressure against the fence throughout the cut, and it consequently pushes the "fence" inward. Even more than that, though, I'm having trouble relocating the fence after every cut in a position that each cut is EXACTLY the same. I set my combination square at 7 11/32" (2 and a quarter for the strip of wood, 5 for the shoe of the saw, and 3/32 for the kerf) and set the fence off that, but I find that there's still a variance. Does anyone have any suggestions on how to minimize (or eliminate) this deviation?

The reason I ask is that I'm making an end table with a top that has plywood strips oriented two at a time perpendicular to each other: ||--||--||--||--

You get the idea.

Thanks for the help,

-Phil Crow

p.s. That two and a quarter was for another piece of the table.

[Silvan]

Maybe clamp pieces of wood in a couple of places along the long side to back up the straight edge, like

+--------|0|--+ | ||| | | ||| | ===0========||| | | ||| | | ||| | | ||| | | ||| | ===0========||| | | ||| | | ||| | | ||| | +--------|0|--+ 0 CLAMPS = WOOD SUPPORTS | STRAIGHT EDGE

If you get the first cut straight, and still have a straight edge, then maybe try using a pair or three of combination squares (or some shop made gauges of some sort) set for the necessary measurement, checked against each other to make sure they're all the same. Clamp them to the edge and butt the fence up against them while clamping it down.

Also be sure the fence doesn't move on one end when you clamp down the other. You might have to make small, gentle adjustments with a mallet after the clamps are snug, but not yet completely tight.

That's about all I can think of. I don't have much experience with doing that sort of work, and there might be better tricks I haven't thought of. The last time I used my circular saw, I was trying to use it to cut down a tree.

[me]

Two thougths:

[Wilson Lamb]

How about a narrow strip with cleats to hold it parallel to an edge? The width would be the difference between the strip and the narow side of your saw plate.

You would put the cleats up against a straight edge and then put on a few clamps to hold it and keep it straight. Since you reference an edge and don't try to mark anything, you should get repeatability.

Of course you will also repeat errors, so it's important to get the guide strip right. You may be able to compensate for some taper by alternating cuts from front and back of the sheet (good blade needed).

[Nova]

If you have a router table cut the pieces slightly oversized. Set the router up first as a jointer to true the first edge. Next set the router table's fence exactly 2" from the bit to trim the stock to size. You'll be cutting on what would normally be the back side of the bit, so remember to reverse the feed direction of the stock and use the appropriate feather boards and hold downs.

-- Jack Novak Buffalo, NY - USA

[CW]

> 2. Build a saw guide.

[Jack-of-all-trades - JOAT]

Mon, Sep 22, 2003, 12:00am (EDT+4) [e-mail] (me) says: 2. Build a saw guide.

I especially like that one. It shows a table saw being used to make one.

JOAT The whole of life is a learning process.

- John Keel

Life just ain't life without good music. - JOAT Web Page Update 20 Sep 2003. Some tunes I like.

[J Pagona aka Y.B.]

Someone mentioned making a saw guide. That's how I would do it.

Attach your straight edge to a piece of 1/4" sheetgood (either plywood or masonite work fine). Use screws every 1' or so. That will stop the straight edge from bowing. Screw from the plywood into the straight edge, and counter sink the holes so that the screw heads do not stick out past the plywood. The plywood should be about 1' wide and 8' long. Attach the straight edge about 6" from the edge. Once the straight edge is in place, run your saw down the straight edge, and cut off the edge of the plywood.

The edge of the sawguide will show you exactly where the saw will cut. To get repeatable 2" thick rips, cut a scrap block about 4" long and 2 3/16" wide. Use this a guage block when clamping the saw guide instead of measuring. Just hold the gauge block flush with the edge of the piece you are cutting, and push the saw guide tight to the back of the gauge block.

These saw guides are even better when you are crosscutting plywood (or wood veneered doors). Clamp the guide over the good side of the cut line, and run a razor knife down the edge of the guide. This will stop tearout on the top of the cut piece.

BTW, if you don't want to use your Borg straight edge for this, you can use the factory edge of a piece of 3/4" plywood.

David

remove the key to email me.

[Nut Tree]

I did not read the rest of the posts to see if some one else suggested this but the best straight edge I have found for cutting down the long side of sheet goods is another piece of sheet good. I have an eight strip from another job but I most often use the second piece of ply, mostly, to act as a straight edge. Then it is only up to your skill with a circular saw to maintain the contact with the edge. I know that the factor edge is not perfect but it is close enough for the cut you get from a circ saw. an eight inch strip gets the clamps far enough away fro the motor housing to get from hitting.

[nct_buyer]

Yeah, I added that just for him to look at. The BORG or Lowes will give you one free cut on a sheet of ply. I figured if he could use that one free cut to get the piece to make his guide.

[Andy Jeffries]

Sorry, do you mean that they charge you to cut the sheets?

Homebase (in the UK) will cut sheets as many times as you want (the guy doing it may not look happy if you ask him to cut a sheet in to 1"x1" squares, but they'll do it).

Cheers,

Andy

[Jack-of-all-trades - JOAT]

Mon, Sep 22, 2003, 10:59am [e-mail] (nct_buyer) says: Yeah, I added that just for him to look at. The BORG or Lowes will give you one free cut on a sheet of ply.

I don't go to Home Depot, unless I'm really, really, desperate. But the two Lowes I get plywood at, the first three cuts are free, then it's 25 cents per cut after. Exccept, they usually forget to charge.

JOAT The whole of life is a learning process.

- John Keel

Life just ain't life without good music. - JOAT Web Page Update 20 Sep 2003. Some tunes I like.

[Phil Crow]

Thanks for the advice, and that there saw guide looks like a hell of a good idea. So the problem of fence deflection is solved. But, is there a way for me to make sure I get the same cut every time, or am I just wanting too much from a circular saw? My goal here is to be able to glue and brad nail all the pairs of plywood together, then glue up all of the pairs into a panel. I realize the harder I work at the repeatablity issue now, the less sanding I have to do later, and belt sanding an eighth inch off of the table will not help the finished product.

'Preciate it.

-Phil Crow

[CW]

[Jack-of-all-trades - JOAT]

Tue, Sep 23, 2003, 12:02am (EDT+4) [e-mail] (CW) claims: Once set, you can do cut after cut with no guide to reposition each time.

I would say that should be correct. However. Always a however. LOL However, I found my circular saw wasn't cutting to the guide for the first six inches or so, it sorta bowed, then it cut a straight line. It's an old saw, and I found the blade wobbles a bit, just a fraction. So, looks like the bearings are a tad worn. But, still works fine, and I don't require the accruacy, so am living with it. But, once it gets about 6 inches into the cut, like I said, it follows the guide beautifully.

JOAT The whole of life is a learning process.

- John Keel

Life just ain't life without good music. - JOAT Web Page Update 22 Sep 2003. Some tunes I like.

[Phil Crow]

Well, I made a saw guide and I tried a few pieces (short cuts) still using my combination square set to the depth (width/lentgth?) I needed, rather than use a stop block. I was able to get good results. The big pain is that it takes about 4 minutes to set the jig, mask the wood (to avoid tearout), SLOWLY make the cut and remove the tape. Doesn't make for exactly speedy work. But, my saw is pretty new, my blade is pretty sharp and my patience is pretty long.

Thanks for the insight, y'all.

-Phil Crow