Problems getting perfectly square boxes. Basic tools?

[Zappacat]

I'm having problems getting my boxes to be perfectly square. I'm building speaker enclosures and guitar amp cabinets out of 3/4" MDF. Initially I had the guys at home depot cut the mdf down to 12" widths with their sliding table saw. I was assuming this process would be faily accurate but it wasn't. What kind of a setup do I need to get nice square straight cuts? So far I have a router, biscuit joiner, 7 1/4" skilsaw and some squares. I'm on a VERY limited budget.

Any help greatly appreciated

[dbhost]

For truly square cuts you need a table saw, or an exceedingly accurate guide system for a circular saw. The "sliding table saw" as you called it at Home Depot is actually called a panel saw. If there was a buildup of dust or debris in the slot, and they rarely clean those things, the cut will be off.

Remember Home Depot themselves post a sign on the cutting station by the panel saw telling customers that they do NOT guarantee the accuracy of their cuts... I use them to rough cut larger panels like full sheets of MDF, or OSB into shorter sections. I CAN cut a 4x8 sheet on my table saw, I do not want to...

[pelligrini]

The cuts I've had HD do for me in the past have never been very good or accurate.

With your tools you can do it a couple ways. A saw/router board would probably be the best shot. You're probably not going to get perfect (perfect is a pretty tall order in my mind), but you can probably get very close.

There's many different ideas for sawboards.
http://www.bt3central.com/showthread.php?t=47899
http://www.finehomebuilding.com/how-...px?ac=ts&ra=fp
http://www.bt3central.com/showthread.php?t=39641

Another way would be to make a router table. For this application it doesn't need to be anything fancy, a thick piece of ply with your router mounted below, and a straight board and a couple clamps for a fence. You'd use the fence as the refrence point to get square.

[LCHIEN]

Straight enough for square boxes consists of several issues.
First, the sides have to be exactly parallel
Second the sides have to be perfectly straight or there will be gaps
Third the corners, all of them, have to be perfect 90 degrees, not 90.2 or 89.8 degrees
Fourth any 45 degree miters have to add up to 90.0 degrees. If you are using mitere corners as opposed to butt corners.
Fifth, the opposing pieces have to be the precisely same dimensions.

While very talented people can do these things with hand tools and hand held power tools, to do this consistently on a weekend warrier basis usually requires standing (stationary) power tools with well tuned rip fences and miter fences and stop blocks.

Some practice obviously helps a lot.

If you can get planed and thicknessed flat lumber (commonly called S2S for surfaced 2 sides) then you can probably get by with a quality Table saw... They do take some room but the imrovement over a circular saw is remarkable.

A quality table saw is one with enough power, enough surface area, and solid fences to do the job. There are some cheap benchtop table saws retailing for aroun $200 bucks retail for sale but those are generally small and have inadequate fences.

A plug for the BT3100/BT3000 saws (the original focus of this forum) may be in order here, these discontinued saws have had a reputation for accurate cuts but they're not for everyone's taste. Hundreds of thousands were sold so there's alot for sale used.

Otherwise, Table saws like Ridgid, and the Delta contractor saws that sell for around $400 new can often be found for a couple of hundred used.

Have HD (or use your circular saw) to break down large panels into pieces about an inch oversize of what you need, then finish them with the table saw.\\

[phi1l]

I have had pretty decent results using one of those aluminum edge guides with a saw-specific spacer.

1) Draw you cut line with a square..
2) put the spacer on the line
3) put the edge guide up against the spacer
4) re-check the alignment
5) tighten the guide clamp
6) remove the spacer
7) make the cut against the edge guide.


Depending on the length/ depth of the cut I use either a 7 1/4" or a 4" cordless saw, so have have 2 spacers, otherwise, I could just attach the spacer to the edge guide & cut out a couple of steps.

With reasonable care I get pencil line width accuracy.

Also, to make boxes, I would clamp or double sided tap the opposite sides together & & cut them at the same time, so they will be exactly the same length.


Then, of course, on glue up, make sure the diagonal lengths are exactly equal.

[Mr__Bill]

Your circular saw needs to be accurate. Test the blade, does it move in and out a bit? Most saws made for the construction market have some slop or play here. Most of the very inexpensive saws even if when new are tight will get some play here after a few hours of use. If yours is one with play in the blade then you will never be able to cut a straight line with it. If you are lucky and it's a nice tight saw, then if you invest in a straight edge it's about all you need if you add in some care and thought.

The straight edge can be one that is self clamping or just a piece of plywood or MDF with a straight edge that you clamp on.

Even if your saw is off you can rough cut and then with the straight edge and router trim it up square. Mark a spot on the router base, assuming it doesn't have a flat side, and keep that spot against the straight edge. Routers don't necessarily have a base that is perfectly round and equidistant from the edge to the bit, so mark a spot and use it.

The square, it may not be. Mark a line on a piece of sheet goods or a kitchen counter top, and then flip the square over and mark it again. Do the lines lay parallel to each other? If not then a great part of the problem is the square. You could spend lots of money on a new one or true up the one you have. Here is an article on how to do it. The other way is to go to where you buy inexpensive tools and take several sharp pencils and test them until you find one that is accurate. Square, pencil, counter top and hope no one yells at you for marking up the counter. The square also needs to have straight edges on each leg

All this is assuming that you are making but joints with the mdf and not trying to make 45deg mitered joints.

Keep asking questions, remember the only stupid question is the one not asked that should have been.

Bill
over here in the rain

[herb fellows]

Plus one on the sawboard, as you say you have a limited budget. I have made a few that were accurate to 1/32" over 2 feet, 1/16' over 3 feet.
If that accuracy level would be ok, it's certainly the cheapest way to go. Just take your time making it, check everything 3 times!

[leehljp]

The way that the older generation made square was with a particular construction technique, beside being cut square.

The key to "square", in addition to the things listed by those above is how to measure:

Measure on the diagonal. Measure the bottom right to top left; Bottom left to top right. These two measurements will be the same when square. Clamp; turn the back side up and measure that side the same way.

Measuring on the diagonals reveals square on a level plane. I am making a set of book cases. One is 1/2mm off of diagonal over a 6' 6" height by 30 in wide carcass. To me that is acceptable.

[Zappacat]

I can't tell you all how much I appreciate your help. I was getting pretty discouraged with this endeavor until reading ALL of your responses. What a great forum! Thank you all very much.

[Zappacat]

Also, to make boxes, I would clamp or double sided tap the opposite sides together & & cut them at the same time, so they will be exactly the same length.

Can you please tell me what you mean by double sided tap? Thanks

[mpc]

Also, how are you measuring/marking the pieces before you cut them? Trying to use a tape measure and pencil to mark them often isn't repeatable enough... after cutting the two boards, stand them face to face on a flat surface and see if they are exactly the same height. I'll bet there is a slight difference. Can't make squares or rectangles if the opposing boards aren't identical in length... you'll get trapezoids at best.

If all you have are hand-held saws, make initial cuts to get the pieces to a workable size. Line the bottoms up perfectly, and the fronts, and tape or clamp them together. Now measure your final length (from the bottom) and and mark it... and cut both pieces at the same time. Hopefully your circular saw isn't a small cordless model with limited cutting depth. By cutting the two pieces together, even if you don't cut exactly to the desired length, at least the two pieces will be identical in length.

How wide are the boards? You might find a benchtop miter saw (aka "chop saw") would be a smart investment. Even a small bladed "slider" model - sliders can crosscut wider boards. Clamp/mount the saw to a flat table, an old door on sawhorses, whatever. Then you can clamp stop blocks to the table so you don't have to mark the workpieces - you just but them against the stop block and cut. Everything will be a consistent size this way. A used table saw will cost about the same as a new sliding miter saw; a table saw will be more versatile in the long run.

The sawboard other folks have suggested is a simple/inexpensive accessory to a circular saw. It helps in so many ways:
* guides the saw
* the edge of the sawboard is initially made by the circular saw so by definition it shows EXACTLY where the blade is going to cut - makes it easy to position the sawboard on your pencil line.
* It helps "back up" the workpiece, reducing tear-out.

A cheaper, but less versatile, accessory would be to make a simple T-square from 1-by material. Make the top of the "T" long on one side, then run the saw along the body of the "T" (the body becomes the guide/fence for the saw) and chop off part of the long "T" arm. Now you know exactly where your blade will cut, just like a sawboard. Line that "T" arm with your workpiece pencil mark and go.

When marking and/or assembling, what are you using as a "reference" square? A framing square? Be warned: many are NOT square. To test: get a piece of MDF since that'll have a quality straight edge. Put the framing square along the edge and mark a perpendicular line using the square. Now flip the square over and mark another vertical line that starts right where the first one intersects the edge of the MDF. If your framing square really is square, the two lines will overlay. If you get a "V" the square isn't square. Using a nail-set or pin-punch to dimple the metal right at the 90 degree corners (either close to the inner corner or near the outer corner) will tweak the square to tune the angle. You can use the same "flip it over" trick to test a carpenter's square. Oh, another good/cheap way to get 90 (and other) angles: the plastic drafting triangles available at office supply stores. They tend to be darned accurate. You'll get 90 & 45 angles, or 30-60-90 angles.

mpc

[ke4fsm]

I believe he means use double sided tape to stick the opposite sides together.

Sam

[leehljp]

Another Tip:

One thing that I did not see above in the second reading, (but I "thought" I had seen it the first time I read through):

Use the SAME rule through out the cutting and building process. Don't change rules, or use two rules, when measuring or you will get different results!

One good trustable rule will help eliminate problems - and then the old adage of "measure twice, cut once" is a great habit to learn.

[cabinetman]

Besides all of the advice given, if you can afford a table saw, that's not the whole battle. Setting it up and using it properly to get accurate cuts would be next in order. Using a router won't guarantee a perfectly smooth edge. There is the possibility of small chattering.

In the "where there is a will, there is a way" department, my first table saw was a handheld circular saw mounted underneath a sheet of plywood, and a straight edge clamped for a fence. Seems kind of archaic, but the principle works.

Keep in mind that cutting/machining tools are hazardous. Improper use could be life threatening.
.

[tommyt654]

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