Exactly Square???

[Mezzanine Rob]

Hi Guys & Gals
I know this is probably a stupid question (Why change habits) I am in the process of making a box and I have to make quite a number of squares and they will need to be exactly square. I am intending to use my trusty LN No.9 and my Shooting Board. My question is what is the process to end up with an true square rather than a trapozide. The squares aren't going to be very big about 75mm square, this is the first time I have tried making a decent box and I am already thinking I should stick to bigger items which can be a little more forgiving.
Can anyone help without embarrassing me too much.

Regards
Rob

 

[Ian down london way]

They can never be exact. What kind of tollerance will be acceptable? 1/2 mm out?

 

[CHJ]

What are you using to prepare your stock and then cut it ?

In the first instance you can do no better than cut the pieces to size and true square.

Any post cutting dressing on smallish pieces be it plane or sanding is prone to create more variations on size and angles.

In my honest opinion on such small pieces your best bet is to spend time and effort fettling your equipment and suitable jigs if necessary to enable cutting to size and true.

If you Have a look at this link and the other pieces of a similar nature in that thread you will see small wood segments that are cut and sized straight off a basic 305mm chop saw that has attention paid to its set up.

If you prepare the width and cut the length to match the width at true 90 deg. then they are square.

 

[Cheshirechappie]

How square your work can be is dictated by the quality of the equipment for checking it. A budget square may not be exactly square for critical work, and using one can only lead to frustration. So, the first thing you must do, if you haven't already, is invest in a really good quality 4" or 6" engineer's square, by a reputable manufacturer such as Mitutoyo, Moore and Wright, Starrett or similar. Buy a new one from a good dealer, don't trust a secondhand one, and expect to pay about £25 to £40. Good ones will come in strongish packaging, which is worth retaining to protect the tool; alternatively, make it a wooden box, so that you can really look after it. You can then ensure that your shooting board is set up to cut square by doing a couple of test pieces, and checking them critically with the engineer's square against a strong backlight. Fiddle the shooting board until it gives reliable, true square, and off you go. Take your time setting up the equipment so that you have confidence in it's accuracy.

 

[GazPal]

Pythagorean Theorum has it's uses and you'll seldom find yourself out of square when setting up if using the 3:4:5 rule. Google is your friend, but arming yourself with simple formulae such as this allows you to calculate/determine square, as well as calibrate squares. :wink:

In terms of shooting for square at 75mm (Or any given size) on a shooting board you could provide for two adjacent guide fence positions at 90 degrees to the fixed fence. One can be set to approximately 78mm for roughing-in and the other at 75mm (Depending on how accurately you make your initial cuts). The first offset can be used in order to achieve square between two adjacent sides and the other to achieve finish size and square when shooting to final dimensions.

 

[jakethebuilder]

Just thought I'd toss this in: You experienced guys are probably already familiar with this. How do you know if your square is really square. You can use a straight edge, something like the edge of a carpenter's level, to check your square. Lay the square against the straight edge, short leg facing the left. Then mark a piece of scrap at the farthest end of the long leg of the square. Then flip the square over, so that the short leg is against the straight edge, pointing to the right. If the square is "true" the long end will indicate the same place you marked previously. If it indicates a different location, you can mark the second location, and then split the distance between the two marks to find exactly square. So, even if you have a damaged or cheap square, you can still determine exact square. Of course, the accuracy is dependent on how straight your straight edge is, how accurately you can mark the two locations, and how accurately you can measure the distance between them, and finally how accurately you can mark the split of that distance. In most instances, the difference won't be very much, even with a cheap square. Not my first choice, but it's a quick way to find if a square is true, as when you find a used one for sale, and want to know if it's worth the price. It's a good idea to check all your squares in this way.

 

[bugbear]

They can never be exact. What kind of tolerance will be acceptable? 1/2 mm out?

If the box is 75mm, I don't suppose the sides are more than 5mm. On those numbers, even if the mitre were a whole degree out, that's only a tan(1) * 5 = 0.08 mm gap (3 thou).

BugBear

 

[marcros]

it is a box made from a number of 75mm squares though isnt it? The cumulative error could start to cause issues

 

[Ian down london way]

That was why I originally asked what accuracy is really wanted. How you cut marketry for a custom box (where the items butt up to each other, but may well have a slim glue line between them, filled by a little white glue and sanding) may well be very different from how you make the sides of a box, vs. preparing to make 20 boxes which need to slide interchangeably into a frame of identical holes.

I wondered if the crispness of the edges, on a small item like a box, may be more imporatant than mass production using a jig and a large saw. If so, then accurate marking, then rough cutting and then careful sanding (e.g. using a right angle guide to the sander) up to a crisp line may well be the order of the day - if you are making just a dozen.

 

[Jacob]

Hi Guys & Gals
I know this is probably a stupid question (Why change habits) I am in the process of making a box and I have to make quite a number of squares and they will need to be exactly square. I am intending to use my trusty LN No.9 and my Shooting Board. My question is what is the process to end up with an true square rather than a trapozide. The squares aren't going to be very big about 75mm square, this is the first time I have tried making a decent box and I am already thinking I should stick to bigger items which can be a little more forgiving.
Can anyone help without embarrassing me too much.

Regards
Rob

Depends on the joints mainly. How are you making these things? There are wheezes and wangles such as having sides overshooting which then are trimmed back to meet the other sides, after they have been glued up.

 

[Mezzanine Rob]

Sorry people, in my ignorance didn't give enough detail.
I am attempting a box a bit like Robert Inghams where lots of square pieces make up the whole.
My veneer squares are going to be a little thicker than his (3mm) I am not using the exact same construction method but I do need to get the pieces as square as I can before gluing to the substrate material.

 

[marcros]

Rob,

there is a thread on here about a walnut veneered kitchen. On it, Jon cuts the veneer en-masse with the table saw to make it square for but jointing. Could you do something similar, so that you set up your saw and the pieces are identical?

Depending on how you are fixing them, the other way is by overlapping them, and using a sharp knife and straight edge. I have only read about this today, so have no first hand knowledge.

Not sure if either helps you- the alternative is probably a shooting board and plane, but you sound like you have a lot to do. All roughly cut to size and stacked a couple or 3 deep though, I bet that you could wizz a lot to size on the shooting board in half an hour which may be quicker than spending endless time setting up other jigs.

 

[GazPal]

Sorry people, in my ignorance didn't give enough detail.
I am attempting a box a bit like Robert Inghams where lots of square pieces make up the whole.
My veneer squares are going to be a little thicker than his (3mm) I am not using the exact same construction method but I do need to get the pieces as square as I can before gluing to the substrate material.

Without knowing much in terms of overall construction detail, I'd assume shooting edges and angles into true would be the route to follow once you've roughed your materials to working dimensions.

 

[Jacob]

I think I'd do a dry run and just fiddle about planing or sanding until they fit.
Didn't our Robbie do an Ingham style box? Unfortunately he has cleared off but you could track him down on the Shaven haven. Here in fact.
Tell him to come home and stop being silly!