I have a plastic box and I want to make a structure which will fit snugly inside. The sides slope down to the bottom of the box and I can't think of a way of (reasonably) accurately measuring the inside bottom of the box.

Any ideas?

 

There are a variety of tools for measuring inside dimensions. What do you have available? What are the approximate dimensions? How accurate do you need the dimension? There is probably as slight filet between the bottom and sides. Can you ignore that and measure just a tad above the filet?

 

The only tool that comes to mind is calipers but I don't have those.
±1mm would good enough.
This is the box in question: https://www.ebay.co.uk/itm/Small-Me...var=572165045751&_trksid=p2057872.m2749.l2649

 

For ±1 mm, I would make a gauge block (e.g., a length of dowel) that was slightly too long, then sand it off little by little until it fits. Telescoping gauges will do the same thing with less effort:


Of course, you need either a micrometer or pair of calipers to get fairly accurate, but an ordinary ruler can also be used.

Just saw your link. For something that big, I would probably use a tape measure that has a given body width (e.g., add 30 mm for inside measurements) for inside measurements or measure the outside and subtract an approximation for the wall thickness. In any event, the curvature where the sides meet the bottom appears significant.

 

Do a McGyver. Just get a strip of paper slightly longer than the dimension of interest, put it inside the box with one end against the box wall, then crease/fold over the other end where it meets the opposite wall.

 

Fill it with water, freeze it and measure the ice block.

 

Do a McGyver. Just get a strip of paper slightly longer than the dimension of interest, put it inside the box with one end against the box wall, then crease/fold over the other end where it meets the opposite wall.

Yes, I like that. Cost zero, and should be accurate enough for the job.

 

Or make your own calipers. McGyver-style.

Use a scrap piece of PCB and cut away a couple strips. Maybe 1/2” wide and 5”-10” long. Or buy a length of aluminum flat stock.

On one end of each, cut away material to make a narrow point.

Go to your local hardware store (where you can buy individual parts) and pick up a short bolt, locking washer and thumb bolt.

Drill the end opposite the points, and drill a hole for the bolt.

Assemble and measure.

I’d only use a drill and motor tool.

 

Since the box is transparent, place a ruler under the bottom of the box and read off the length of interest.

 

Since the box is transparent, place a ruler under the bottom of the box and read off the length of interest.

D’oh! I missed that transparent thing!

 

Fill it with water, freeze it and measure the ice block.

Providing the freezing doesn't split the box. I don't think the box would stand a 9% expansion.
http://www.iapws.org/faq1/freeze.html

 

Since the box is transparent, place a ruler under the bottom of the box and read off the length of interest.

As Captain Mainwaring of "Dad's Army" would say, I wondered who would spot that first.

 

A single piece of tape, with an xacto knife. Push the tape into the corners on one side of the box with a putty knife, then cut the tape with the xacto lift and measure. The opposite side will be the same.

kv

 

Providing the freezing doesn't split the box. I don't think the box would stand a 9% expansion.
http://www.iapws.org/faq1/freeze.html

It won’t be a problem if the ice can move into an opening. Anything wider than it is tall should be fine.

 

Measure the outside. Measure the thickness of the walls. Subtract. Do your area formula.

 

Measure the outside. Measure the thickness of the walls. Subtract. Do your area formula.

Except for the problem that most molded parts are made thicker in the rounded corners for strength.

 

Since the box is transparent, place a ruler under the bottom of the box and read off the length of interest.

That will likely not work if the measurement needs to be within 1 mm of the true value. The refraction of the light, particularly at the corners, will probably introduce an error significantly more than that.

 

That will likely not work if the measurement needs to be within 1 mm of the true value. The refraction of the light, particularly at the corners, will probably introduce an error significantly more than that.

Actually the meeting of sides and bottom is very small radius so It will work well.

 

I have a plastic box and I want to make a structure which will fit snugly inside. The sides slope down to the bottom of the box and I can't think of a way of (reasonably) accurately measuring the inside bottom of the box.

Any ideas?

For cases such as this, I always use wooden sticks and cut them to the exact length that will fit in the box's top and bottom. Then I measure the sticks. The real challenge is the box's radius at the edges and corners. Only way I can think of solving that would be to cut cardboard circles and see which one fits best.

 

A third stick would be needed to accurately measure depth.