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View Full Version : Semi-OT: Making a Straight Edge / Saw Guide?



Fasttrack
01-08-2013, 10:09 PM
Well, I never did buy a table saw. Its still on my list but other expenses came up and it didn't take me very long to fill my basement with machine tools. Consequently, I no longer have room for the Delta Unisaw I was lusting after. I did pick up a Skil Mag77 worm drive circular saw that I absolutely love. I've also got a number of 3/4" sheets of high quality oak veneer plywood here to build some heavy duty bookshelves for my sister.

I've got a piece of steel channel that is 5' long and reasonably straight but I'd like to make an 8' straightedge to facilitate cutting the sheets of plywood. Any suggestions? I considered ripping a 4" or 5" wide strip from a factory cut sheet and using the factory cut edge as the guide but I'm not sure how straight/flat the factory cut is. Am I being too picky about this? Just do it in two setups with the 5' edge and hope for the best? Stop being a tight-a@@ and just buy an 8' long piece of steel tubing?

Just to reiterate, I do not have a table saw. I'm trying to make do with a nice circular saw. I want this to be "furniture quality" and not "construction quality" - not an entirely simple task given only a circular saw. I also have a tiny trim router meant for trimming laminate on counter tops, if anyone can think of something clever with that.

Duffy
01-08-2013, 10:48 PM
Buy SOMETHING about 3-4" wide and 8' 6" long, and preferably 3/8" or so thick. Steel, plastic, dry straight lumber, whatever. It needs to be longer than the plywood for an accurate lead-in. Equally important, get a pair of horses, mount 4' tops on them and a BUNCH of 2X3s to act as a fully supported cutting table. With the saw set at an inch depth, cut across or along-does not matter. Now you can cut. How to deal with splintering of the veneer is ANOTHER problem, particularly on cross-cuts. Scoring with a sharp knife is the best bet, but requires CAREFUL coordination between score line and cut line. Rotsa Ruck!:D

firbikrhd1
01-08-2013, 10:49 PM
My dad was a finish carpenter for a great many years and was able to use a circular saw well enough to make cabinets, teak chests for yachts, install paneling without moldings at outside corners by cutting the panels at 45 degree angles and many other jobs that required very straight, accurate cuts. This was done by using a piece of aluminum flat stock a little over 8' long, 2 1/2" wide and 3/16" thick. He would measure the distance from the edge of the shoe on his saw to the edge of the blade (depending upon which side of the blade he was cutting to take the kerf into account, add that to the desired width, clamp the straight edge in the proper place with heavy spring clamps at each end to achieve the desired cut and make the cut. He always depended upon the factory edges to be straight but eyeballed them as well just to be certain, particularly for boards. The nature of plywood makes it more stable and less likely to change shape after it leaves the factory, particularly in higher grades of material. If squareness was critical on the ends of a full sheet of plywood he would check them with a framing square before cutting or measure a 3-4-5 triangle. Any minute adjustments for close fits were made with a block plane. Today I still have oak paneling in one room which ahs joints at the outside corners that re difficult to discern and the grain from the sheet that was cut continues around the corner. He always liked to say that when he finished he wanted it to "look like it grew there".

Another thing he did is make a custom saw guide using a piece of flat bar that fit the saw guide slot for his saws with a hardwood end similar to how a "T" square is made. The wooden cap of the "T" was about 18" long and the flat stock a little over 2' long. He could use this just as he would any saw guide but by paying close attention to how the "T" ran along the edge of a piece of material he could accomplish remarkably straight cuts up to half the width of a sheet of plywood.
I have adopted these methods as well and they work very nicely even if it takes more fiddling and time than having a table saw. If you are interested I will post a photo of his custom saw guide design.

Regarding splintering along the edge of materials as they are cut, if they are cut from the back side they typically don't splinter. This requires careful measuring and being certain you have the material marked in a "mirror image" of how it will actually fit. It's very easy to mess up and waste a lot of material using this method until you become familiar with it if intricate pieces are made.

Tony Ennis
01-08-2013, 10:55 PM
The edge of a piece of plywood is about as straight as it gets. You'll be able to make nice cuts. You won't be able to make very repeatable cuts, in the scheme of things. That being said the Olde Guys did it all with hand tools so you ought to be fine.

When cutting large plywood sheets I prefer a circular saw and a plywood edge. The reason is that it's really hard to properly control a sheet of plywood when you're trying to feed it into a saw. It also requires a crapton of shop space.

Fasttrack
01-08-2013, 10:56 PM
If you are interested I will post a photo of his custom saw guide design.

Yes! I'm interested ... I didn't consider doing it that way. I've had marginal success with a really cheap circular saw so I'm optimistic about what I can achieve with the Skil saw. That said, I'm no carpenter and certainly not as skilled as your father! Good to know it can be done, though.

Thanks for the tips, guys. I did some work with a 4' by 4' 1/2" oak veneer plywood for my bathroom remodel and used a high end plywood blade. It didn't splinter the veneer at all and I cut it just as you suggested, Duffy, with 2X4 underneath it. Problem was, my fancy blade was mounted in a $29 circular saw. It barely had enough power for the 1/2" thick stuff and the base was so flimsy that it was hard to cut straight even with the 5' straight edge.

firbikrhd1
01-08-2013, 11:09 PM
Yes! I'm interested ... I didn't consider doing it that way. I've had marginal success with a really cheap circular saw so I'm optimistic about what I can achieve with the Skil saw. That said, I'm no carpenter and certainly not as skilled as your father! Good to know it can be done, though.

Thanks for the tips, guys. I did some work with a 4' by 4' 1/2" oak veneer plywood for my bathroom remodel and used a high end plywood blade. It didn't splinter the veneer at all and I cut it just as you suggested, Duffy, with 2X4 underneath it. Problem was, my fancy blade was mounted in a $29 circular saw. It barely had enough power for the 1/2" thick stuff and the base was so flimsy that it was hard to cut straight even with the 5' straight edge.

I'll be happy to take a picture some time tomorrow and post it for you.

A cheapo circular saw probably won't yield great results regardless of how great the blade is. A quality saw has enough weight to prevent it from vibrating and bouncing along as well as a solid shoe instead of a stamped shoe. Dad's saws are incredibly heavy by today's standards. They are all aluminum housing Black and Decker saws that he bought when I was in my mid teens. I'm almost 60 now and he still has and uses those saws. The brushes have been replaced a few times as well as bearings and an armature I believe as well, but weight and all i still love it when I get the opportunity to use one. They are very smooth running and as previously stated, hefty, even the 7 1/4" one.

darryl
01-09-2013, 12:14 AM
I would go aluminum instead of steel for the guide bar. It's nice to be able to use a tube, but you do have the issue of clamping it tightly enough that it doesn't move. Tubing has enough give since it's hollow that it might slide on you- otherwise that would be my choice. And you do want at least 3-4 inches past on either end, so a minimum of 8 ft 6 in length.

If you go with flat bar, I'd choose some 3/8 by at least 2 wide. That's enough height to prevent the base from any tendency to ride up over it, and it will be rigid enough on the flat that it doesn't bend if you exert side pressure against it.

For any significant amount of cutting, you might be well advised to construct a 2x4 support (will look a bit like a piece of framed wall). To do a good job you will need to support most of the area of the sheet while you make the cuts. If you make it about 7 ft 8 long and 3 ft 8 wide, there will be enough overhang of the sheet in either direction to allow for the clamps to hold the straightedge. You can screw this together so if needed you can take it apart and use up the material in any way you want to.

elf
01-09-2013, 12:22 AM
Buy SOMETHING about 3-4" wide and 8' 6" long, and preferably 3/8" or so thick. Steel, plastic, dry straight lumber, whatever. It needs to be longer than the plywood for an accurate lead-in. Equally important, get a pair of horses, mount 4' tops on them and a BUNCH of 2X3s to act as a fully supported cutting table. With the saw set at an inch depth, cut across or along-does not matter. Now you can cut. How to deal with splintering of the veneer is ANOTHER problem, particularly on cross-cuts. Scoring with a sharp knife is the best bet, but requires CAREFUL coordination between score line and cut line. Rotsa Ruck!:D

Add a sheet of rigid foam insulation on top for an even better cutting table.

Arcane
01-09-2013, 12:30 AM
How about what this guy has? The nice thing about it is the edge where the blade runs can be aligned exactly where you want the cut.

http://www.youtube.com/watch?v=2_2hypJNYRQ

kendall
01-09-2013, 02:35 AM
How about what this guy has? The nice thing about it is the edge where the blade runs can be aligned exactly where you want the cut.

http://www.youtube.com/watch?v=2_2hypJNYRQ

The method shown in video link will work, but the easiest way possible is to freehand a 1, 2 or 3 inch strip of plywood, screw or glue it along the edge of the rest of the sheet with the factory edge towards center, then set your saw to depth and cut it. No need to measure or set position, the factory edge gives a straight cut line, and the edge of the guide will be right at the blade. Changing blades can shave the edge, but seldom enough to effect woodworking accuracy

uncle pete
01-09-2013, 03:59 AM
I use about the same idea as that video link Arcane posted. Once your guide is built it's dead simple to use, Measure your stock and mark it at each end, line the guide up on your marks and cut. Nice clean straight cuts to the accuracy of your measuring ability. A high end panel saw might? do a better job, but I can't ask for much better with that guide and a cheap $100 Dewalt saw.

Your material is fairly costly. I'd certainly buy a blade designed for that type of veneer cutting. Stock blades that come with these saws aren't the best.

Pete

taydin
01-09-2013, 04:14 AM
I used to keep a 3m long aluminum rectangular tube, 100x50x2mm, around for these types of cuts. Just put pieces of 50mm or so hard foam on the floor, fix the tube to the MDF (or whatever) sheet using two clamps at each end and start cutting. If you want to prevent tearout on the surface, use a blade that is specially designed for cutting laminated stock. The teeth on these blades alternate between rectangular and trapezoid shape. Also, do the cut in two stages. First, adjust the saw to 1mm depth and make a scoring cut. This cut needs to be done in the "climb milling" direction, so hold the saw really tight so that it doesn't run away from you! Then adjust the depth to about 1mm more than the sheet thickness and make the actual cut. This cut will be made in the "conventional milling" direction, which is the usual way.

This scheme simulates the operation of a scoring table saw, but the setup is a little difficult because of the climb cutting. But you can do the scoring cut using convention cutting, too. Because the cutting depth is just 1mm, the chances of tearout will be reduced a lot.

Lew Hartswick
01-09-2013, 08:14 AM
An IDEAL straight edge for that purpose is a chunk of "Uni Strut" . I have a 9 ft
a 5 ft and several shorter pieces and even "invented" a clamp so that no part
of it sticks up to interfere with the saw. I used P 3300 . I did the calculations
for deflection in the lateral direction for them at the time but can only find it
for the P 4100 at the moment (that is the smallest one) and that is only
0.006 in. per pound of lateral force. If you want a pic. of the clamp I designed
I'll take a few pix and post (probably start a new thread for them)
...lew...

Bob Fisher
01-09-2013, 01:08 PM
I always cut full sheets with a circular saw as opposed to the table saw. I have always wanted to build a panel saw, but don't have the room for one, so I use guides like have been suggested. Most often, I will have the box store cut them for me, they can at least reduce a sheet to manageable sixes for the table saw. Bob.

Paul Alciatore
01-09-2013, 01:54 PM
Talk about coincidence, I have an almost identical project in my garage/shop right now. Five sheets of oak verier plywood that I need to cut into strips for bookshelves for my office. I do have an inexpensive table saw as well as a handheld circular saw. The problem with cutting whole sheets of plywood with a table saw is you need to extend the table for about 5 or 6 feet both front and rear and for several feet to the side in order to support the full sheet. In short, it would take up almost the entire garage. I saw one like that in a cabinet shop once and it was very large. I set up a radial arm saw with side supports once, but it was about 20 feet wide. Still smaller than the table saw setup. I added swing out arms to support plywood sheets to the front. It worked, but took up a lot of area that I do not have in my garage.

For my present project I found some scraps of particle board shelves from a previous shelf project. They are 8' long and about 4" wide and appear to be stiff enough and straight enough to serve as a saw guide. I will clamp them on the oak plywood and run the circular saw against them. I believe it will work OK. If I have a problem with the first cut, I can just go buy a 12" wide particle board shelf and use that.

I am presently making some false tops for my plastic work horses so I can just cut through the plywood while it rests on them. I am using some scrap 2x6s and more of the scrap particle board strips. I have to work in the driveway as my garage/shop is too disorganized at present and have been rained out for several days now. That's OK as the state needs the rain.

I will post pictures and results here.

tylernt
01-09-2013, 03:23 PM
I found some scraps of particle board shelves from a previous shelf project. They are 8' long and about 4" wide and appear to be stiff enough and straight enough to serve as a saw guide. From what I understand, products like MDF and particle board are pressed into something like a die and come out extraordinarily flat and straight (well, by wood standards, anyway). I'd favor MDF over particle board for this purpose, ideally one with a melamine edge, but if you already had it then the price can't be beat!

Lew Hartswick
01-09-2013, 04:08 PM
Here are the clamps I made for using Unistrut for a saw straight edge. Been
working for over 15 years.

...Lew...
http://home.earthlink.net/~lhartswick/2013-Jan-09%20001.jpg
http://home.earthlink.net/~lhartswick/2013-Jan-09%20002.jpg
http://home.earthlink.net/~lhartswick/2013-Jan-09%20003.jpg

firbikrhd1
01-09-2013, 04:08 PM
Yes! I'm interested ... I didn't consider doing it that way. I've had marginal success with a really cheap circular saw so I'm optimistic about what I can achieve with the Skil saw. That said, I'm no carpenter and certainly not as skilled as your father! Good to know it can be done, though.

Thanks for the tips, guys. I did some work with a 4' by 4' 1/2" oak veneer plywood for my bathroom remodel and used a high end plywood blade. It didn't splinter the veneer at all and I cut it just as you suggested, Duffy, with 2X4 underneath it. Problem was, my fancy blade was mounted in a $29 circular saw. It barely had enough power for the 1/2" thick stuff and the base was so flimsy that it was hard to cut straight even with the 5' straight edge.

OK, here are a few pictures of a saw guide like my Dad made. This one is mine.

http://i283.photobucket.com/albums/kk287/firbikrhd1/P1090069Small.jpg

http://i283.photobucket.com/albums/kk287/firbikrhd1/P1090070Small.jpg

http://i283.photobucket.com/albums/kk287/firbikrhd1/P1090071Small.jpg

Arcane
01-09-2013, 04:37 PM
Run a skill saw along the long edge of a drywall T square and and cut off the short bit that sticks out. You now have a square you can clamp to a 4 x 8 sheet and make a 90 degree cut with just one measurement for length, aligning the now cut off end with where you want your cut to be.

kwoodhands
01-09-2013, 06:10 PM
Make your straight edge this way. 12" rip of 1/4" masonite or plywood with a 3" rip of anything straight,plywood,mdf, wood ,metal etc. Fasten the straight edge 2" from one edge. Screw thru the 1/4" stock to the straight edge making sure the screws are countersunk.
Now install a combination blade with 36 or more teeth. Run the saw against the straight edge and thru the 1/4" stuff. You will rip off about 3/8" if you are using a worm drive skilsaw.
Now you can rip the other side with the wide side of the saw base, if I recall it is 4 -7/16".
You have a straight edge that you clamp exactly to the cut line ,from either the narrow or the wide saw base. Usually no chipping happens on the straight edge side of the sheet.Might chip on the unsupported side.
Do not score or tape the cut line,does not always work. Instead make a scoring cut first,then the thru cut.To make a scoring cut, set the base to a 1/8" or so depth of cut. Set the saw with the guard pulled up at the end of the stock as for a pulling cut. Another words start at the wrong end and pull the saw backwards.You have to lift the guard for the first 1" of cut or the guard will hit the end and prevent pulling the saw backwards.
As soon as you pass the end let the guard go down,it will hit the masonite.Keep the saw base against the straight edge as yuo pull the saw backwards.When done,set the saw so the teeth protrude 1/4" or more thru the stock and then cut forward as normally.
This method is safe, it works, it prevents chipping in plywood,veneer stock,plastic laminates etc.
It is also much faster and more accurate than scoring with a knife and using masking tape.
Do not use a plywood blade for 3/4" sheets. Their are too many teeth and the blade will heat up and wobble. These are fine blades for 1/4" stock but not for 3/4". A good choice would be a combination blade, with a 7-1/4" blade I think no more than 40 tpi.
One other thing, I always rip from the narrow edge of the saw base,I have had problems keeping the wide side of the base tight to the straight edge. It would seem that the wide side would be best,no chance of the saw tipping. Never worked for me.What ever works for you is the best way.
The scoring method works for cutting down doors too if needed.
mike

kendall
01-09-2013, 07:29 PM
Here are the clamps I made for using Unistrut for a saw straight edge. Been
working for over 15 years.

...Lew...
http://home.earthlink.net/~lhartswick/2013-Jan-09%20001.jpg
http://home.earthlink.net/~lhartswick/2013-Jan-09%20002.jpg
http://home.earthlink.net/~lhartswick/2013-Jan-09%20003.jpg

Very nice clamps Lew, they look like they'd be great for clamping wide glueups flat too

uncle pete
01-09-2013, 07:49 PM
Lew,
My thanks for posting those links to your clamps. Pretty clever in my opinion.

Pete

Fasttrack
01-09-2013, 08:30 PM
Wow - a lot of great information here. Thanks guys!

Lew - those clamps look great. I was thinking last night about making something out of aluminum/steel and drilling and tapping holes every 6" for some lever action hold down clamps. Never thought about Unistrut - that's a great idea.

Thanks again fellas, I feel a lot more confident about my project knowing that there are plenty of legitimate woodworkers who use circular saws. I'm a slow worker with all my other projects, but when I get it finished, I'll post some pictures.

Robin R
01-09-2013, 10:10 PM
If you don't mind spending a bit here is a ready made option. http://www.leevalley.com/en/Wood/page.aspx?p=41707&cat=1,240,45313&ap=1 It has an option of clamps like Lew Hartswick made up, these run in a T slot that runs the length of the guide. There's also an optional traveller, this holds the saw against the guide so you can keep your other hand clear of the blade. Another nice feature of the guide is that you fasten a piece of 1/4" ply to the bottom, once the saw is fixed to this you carefully plunge the saw through this, giving you an anti chip-out feature.

Now if you really want to splurge, this would be worth a look. http://www.leevalley.com/en/Festool/page.aspx?p=68072&cat=5,105,68332 A guy I do a lot of work for has one of these and he really swears by it, it has a non slip guide rail that you don't even need to clamp, as well as a zero clearance base that largely eliminates chip-out.

Frank46
01-10-2013, 01:12 AM
I'm one of those people who cannot cut a straight line with a saw. They do sell this gizmo that is 2 4' pieces of extruded aluminum and some clamps that clamp the straight edge to whatever you are cutting. All you have to do is figure out the offset. The distance from the outside of the saw blade (tape measure comes in handy) then position the gizmo plus the offset of the blade and then cut. Worked great when cutting down the height of some doors I had to install. Good straight cuts and cleaned up nice with a belt sander. Frank

boslab
01-10-2013, 04:29 AM
I tend to use plasterers feather edge, aka 'Darby, these are found at builders supplies, they are hollow extruded Ali rectangular box sections the lengths are available in 2 sizes, short 4' and long 8', pop off the end caps and stick the clamp inside.http://www.google.co.uk/search?q=plasterers+feather+edge&hl=en&tbo=d&source=lnms&tbm=isch&sa=X&ei=YInuUOnRHvST0QXc94HQCQ&ved=0CAYQ_AUoAQ&biw=1024&bih=673#biv=i%7C18;d%7CqRqhkzgtP3cO0M:
Mark

Lew Hartswick
01-10-2013, 08:23 AM
Now thats interesting.
<http://www.leevalley.com/en/Wood/pag...240,45313&ap=1 (http://www.leevalley.com/en/Wood/page.aspx?p=41707&cat=1,240,45313&ap=1)>
I wonder when that was invented/released??
The clamps I did was at least several years before I retired which was a bit
over 15 years now, so on the order of 17 years ago. Guess I should have
sold the idea to someone. :-)
In any event if youre a "hsm" and Unistrut is available it's a LOT cheeper.
...lew...

JoeBean
01-10-2013, 01:13 PM
I use a track saw, which is essentially what you guys are talking about here, that I use in cabinet making. I've used the Makita and Festool, but I bought the DeWalt because of the Makita's tendancy to leave tearout and the Festool being underpowered (and overpriced!), and it had a couple other features I like. It's much easier to use than a table saw unless you have a LARGE slider, which takes up so much room it's impractical for me.



Anyway, here are a few things I've noticed that I'd try to incorporate in a design if I were to DIY it. Forgive me if I'm repeating something as I never read the entire thread:
The track saws essentially lock into position, with adjustments to keep it tight to the track. I think a fairly simple design that would perform similarly is if you have a jig on the saw that wraps around to the other side of the straight edge you're using and hold the saw tight against it, with plastic slides.


Having "splinter guards" in place that essentially act like zero clearance inserts in a table saw is surprisingly important if you want to avoid tearout in sheet goods. You could easily DIY with some wood and some way to mount it to the circ saw


Being able to plunge is really convenient, particularly for partial cutouts. If your saw won't allow that, it should be simple enough to make a mechanism to do it with a spring return and an adjustable depth stop.


If you're using it for any amount of time plan with sheet goods on making 2 guides, one about 52" long and another about 100" long (assuming a 4x8 sheet). You'll kick yourself if you have to use an 8'+ long guide across a 4' sheet more than once. And unless you have a great design for quickly joining 2 guides together so they're straight and solid don't bother with connecting 2 short guides.


On the topic of guides, Mafell makes a really cool flexible track system that you can roll up. Supposedly it works really well, but I've never seen it myself. But it would be a great feature if you could figure out how to do it effectively.


Finally, one of the simplest platforms is a simple 2" sheet of styrofoam. Lay it almost anywhere, including across sawhorse platforms, and it supports well and holds the sheets in place. Just make sure to adjust the blade so it's not sticking too far into the styro or you'll get buildup on it. Also, I spray my blade with boeshield regularly during cuts to avoid that and to aid blade life (something I first read about here, IIRC). Seems to work well!