I’m a newbie, taking up this fine hobby late in life (60s). By nature, I’m an OCD type of person, which can be a blessing and a curse.
I’m building small boxes on a Dewalt jobsite saw, which I have tuned to the best of my ability. I have watched countless videos on cutting miters and have Doug Stowe’s book.
I check my 45s on a Starrett combination square and they look right on. I do a dry fit and everything looks good. But when I apply glue and roll ’em up, I almost always get one corner that is out of square. I use a Starrett machinist’s square to check. I usually apply tape (like Mr. Stowe) as a clamp. I have a Bessey strap clamp, but haven’t had great success with it.
What is so frustrating is it happens so consistently! It’s not off by a mile, but just the fact that it is off bothers me. Would anyone ever notice? Not unless they put a square to it, but I really want to get it right.
When I check for square measuring the diagonals, they match up, so I’m at a loss.
Any suggestions before I drive myself nuts?
Thank you kindly!
Replies
Just wanted to add that these usually use panels for top and bottom, then I cut off the lid.
Ford, it is wood, no one will notice if something is very slightly not square. As long as the joints are nicely closed and everything fits don't worry. That being said I just made a drawer with HC dovetails that was out of square that caused me a lot of grief when I tried to install it as a flush mount. Functional not cosmetic. I ended up shimming the slides and hand planing a slight misfit front to get a nice fit. Consider what are you trying to make, a beautiful item or something that is +/- 0.001".
Doing miters on boxes like that are huge pains in the butt. Being off a tiny bit gets magnified as the number of bevels increase. The only method that works for me is fine tuning with a shooting board.
I'd rather dovetail corners than miter them. Much less frustration. But that's me.
It is difficult to get a precise fit. That said try overshooting the 45 degree corners a bit. Use something like 45.3 degrees. That way the outside edges (show edges) will meet and the corners can be compressed together. It works. Also make sure your cutting process insures you get equal lengths.
Yes it's frustrating. My number one cause of this is a slight difference in the length of one or more sides. Even with stops set on my table saw, I can get a little off. Number two is the workpiece moving just a bit through the cut so it's not 45 in the vertical. Cutting twice helps with that. Number three is finding that one or more of the sides has become not flat - a slight curve throws it off.
I bit the bullet and made some shooting boards, but sometimes you're chasing your tail. I've resorted to filling the gaps with thin strips if they're too noticeable.
Some of the things you mention cause me to question how you are cutting your pieces. If you are using the throw away miter gauge that came with your saw to guide your crosscut you will never solve your problem. Either invest in a high quality miter gauge or for even better precision build a sled.
As for your pieces cupping, I would ask what your wood sourcing and acclimatization process is? Most wood needs to acclimate to your shop environment after purchase and before milling, this allows the wood to stabilize. Are you purchasing rough sawn hardwoods and milling it yourself or S4S from a big box store?
Last but far from least I always shoot a critical miter for the ultimate precision. There is an article on FW that shows you how to make an excellent shooting board specifically for case miters. Using this board I have successfully joined case mitered cabinets upto 21" wide.
https://www.finewoodworking.com/project-guides/shop-projects/a-shooting-board-for-case-miters
I did get rid of the toy miter gauge and upgraded to a Fulton, which came with a fence and you can adjust the bar so there is no play. It's not top of the line, but a big improvement. To that I attach a sacrificial fence, set the angle to 45 (check it) and make the cuts (checking them) with the blade at 90 degrees. My boxes are small, usually only a height of 2 inches. For larger sizes, I'd have to make a sled and tilt the blade, but I haven't done that yet. I use stop blocks and clamp the work piece to the fence to keep it secure. I'm using a Freud 60 tooth thin kerf crosscut blade.
I'm not set up to do any milling, so I get my boards from an online source. Because I'm working small, 24" boards are long enough. Usually 4"-6" wide, 3/8" thick. I get them from Ocooch Hardwoods, they are sanded to 150 grit, "project ready." I unpack and let them sit in my garage (shop) with stickers between each board.
I don't have a good plane, but when I do, a shooting board will be next!
https://ocoochhardwoods.com
If you do a dry fit and it is perfect to your eye it should come together with glue. I never liked the masking tape technique for closing miters, I like to be able to apply pressure evenly and in all directions to control slip in the joints, for that I use a 4 way clamp at the top and one at the bottom.
https://www.leevalley.com/en-ca/shop/tools/hand-tools/clamps/31162-veritas-4-way-speed-clamp?item=05F0101&utm_source=free_google_shopping&utm_medium=organic&utm_campaign=shopping_feed&gclid=CjwKCAiAkrWdBhBkEiwAZ9cdcOMtbnG_o8xdsziHhlTDR8DtdgEC_nZwCHzeIFzw39YerpBBeagOVxoCIDwQAvD_BwE
What Stantheman said.
Slight differences in side lengths have been my nemesis. I now put the opposing sides back to back to confirm that they are precisely the same length. If not, I saw the longer one again using the same stop.
For me the objective is precision rather than accuracy. Box dimensions are negotiable.
Remember there are 2 angles that have to be dead on to get a perfect roll up - Mitre face must be 45 deg to the face of the box side, and the edge of the mitre must be 90 deg to the edge of the box and exactly parallel with the mitre at the other end. So all four box sides must be exactly the same width and thickness. If not, you could get equal diagonals at the top of the box, but the sides could still be off square inside the bottom, where you can't check. You say you're a Newbie so maybe you don't have a thicknesser - I think you call it a planer over your side of the pond - to make sure. Even if mitres are 45 deg dead on, if the cut is not exactly 90 deg to the top and bottom edge of the box side they won't roll up square - and, as previously mentioned n this thread, the errors magnify x 4 ( or is it 3?).
Being in UK, where table saws are, sadly, a bit like hen's teeth, I also use a mitre saw (DW717) for my boxes and cut the mitres with the box sides on edge (i.e. 90 deg cut is vertical). The 45 deg preset was perfect in both directions straight out of the box, but I take great care making sure the stock is parallel in thickness and width, the vertical cut is dead square to the base of the table, the rear fence is also dead square vertically to the table and I use a stop to get exactly equal lengths. I hand hold the workpiece and, probably most importantly, turn off the saw and let it stop before removing the workpiece - thus avoiding any chance of the saw blade grinding off any wood from the mitre (or flesh from my hand!) after the cut. Cut down slowly with a sharp blade and it works.
And you thought you were OCD!! Hope that helps, and Happy New Year!!
I use these without the plastic inserts, 1 top & 1 bottom on small boxes They tighten with one handle and self-balance the pressure if you keep them waxed:
https://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/pages/merle_clamp.html
To tweak individual corners I use turnbuckles captured in blocks to open & shift small diffs.. see photo. Tough to use this method with the top & bottom captured on glueup tho'.
Maybe try splining the joints and using the 4-way clamp Gulfstar mentions. Or build your own.
Corners? We don't need no stinking corners.
Thanks for all the feedback, I really appreciate it. I'll keep your advice in mind as I go through the process. It's helps knowing that is not just beginners like myself can find challenging. Probably the first thing I'll do is put that square away so I don't get frustrated because it's not perfect. As long as it's pretty darn close, that's good enough! I'll keep working at it...happy new year!
The Dewalt Job Site Saw is a very good saw for it's price point and intended purpose.
I would "guess" there is run out and machine tolerances potentially coming into play here.
Yes indeed, I've considered that. The aluminum table isn't even flat and that coating makes fitting miter bars tricky. I wound up sanding it off the miter slots. Tamar on YouTube has a video about getting the best performance out of this saw. She eventually ditched it for a Saw Stop. I'll keep with this one for now and see how it goes. Happy new year all!