when is a hole not a hole

[KREW2]

Well, maybe it is still a hole but no good if it isn't the right size.

I was drilling nylon/Plastic chopping boards to make spacers for a launching trolley axle of 25ml.
After cutting 6 I decided to test the fit and the centres were too small. The cutter was clearly marked 25ml, but the holes cut were only 24ml in diameter.
I thought there was a mistake in the size of a 25ml hole cutter I bought, so I took it back to Tool station, they had no hesitation in changing it for a different brand, low and behold it was exactly the same size so I didn't bother, and popped next door to Screwfix. Armed with my vernier I asked for a 25ml hole cutter, only to be confronted with exactly the same dilema, the widest part of the cutter was the toothed edge and only measured 23. 6 diameter.
What do I have to do to get a 25ml hole

 

[pvb]

What do I have to do to get a 25ml hole

If you get the depth and diameter right, your hole will hold exactly 25ml.

 

[Dipper]

I've got something similar to this. I've used it on chopping boards and GRP. Adjust it to the size you want. There aren't many that go down to 25mm though. This one does.

 

[Poignard]

(...).
What do I have to do to get a 25ml hole

Some of the products sold by cut-price outfits are not of very high standard. I should think a Starrett would be accurately sized but expensive, especially if you're only buying it for this one job.

What you could try is to buy a cheapo from Toolstation and bend the teeth outwards by 1/2mm.

 

[NormanS]

A round file?

 

[KREW2]

A round file?

It's not depth I want its diameter. Strangely the cutter marked 28ml cuts a 28ml diameter hole.
I have been using a round file but after doing 2 of 24 washers I got fed up.
Splaying out the teeth is an option I am going to try today.

 

[Norman_E]

If you use a drilling machine try a 25mm Forstner bit instead of a holesaw. Alternatively buy a 25mm blacksmiths drill. That is a twist drill designed for metal, with a reduced size shank to fit into a 13mm or half inch chuck. Some plastic boards cause a drilled hole to close up slightly when the drill is withdrawn and a one inch drill (25.4mm) may be a better option.

 

[Deleted member 36384]

Dont trust squares bought from modern franchise tool shops and DIY stores, even branded quality items are not a right angle with many running off by 1mm over 6''. I bought a calibrated Engineers Square and tested a few I had at home and all were not true.

 

[reeac]

Dont trust squares bought from modern franchise tool shops and DIY stores, even branded quality items are not a right angle with many running off by 1mm over 6''. I bought a calibrated Engineers Square and tested a few I had at home and all were not true.

If it's a simple steel engineer's square then you can adjust it by using a hammer and punch applied to the appropriate point at the corner. There's a U tube video that shows how. Pretty impressive, I thought.

 

[DanTribe]

You can sometimes gain a bit of wriggle room by "wobbling" as you drill.
Obviously you can't do this if using a pillar drill, only if using a hand held.
A bit of a bodgers approach but probably not critical engineering for trolley wheels.

 

[penberth3]

It's not depth I want its diameter. Strangely the cutter marked 28ml cuts a 28ml diameter hole.
I have been using a round file but after doing 2 of 24 washers I got fed up.
Splaying out the teeth is an option I am going to try today.

Already pointed out at Post #2, it's mm - you don't measure diameters in millilitres!

 

[Fr J Hackett]

I have a Starrett 1" and have just measured it and it is 0.975" although it has had a lot of use I expect that it would cut a hole close as dammit to 1"

 

[Deleted member 36384]

If it's a simple steel engineer's square then you can adjust it by using a hammer and punch applied to the appropriate point at the corner. There's a U tube video that shows how. Pretty impressive, I thought.

Thanks, did not know that, I do have one inaccurate steel set square. The other inaccurate ones are wood / brass assemblies for wood working. The Engineers Square is certified as right angle to some British Standard. I tested my set squares from collage draughting days against it and they are all accurate, so it really is just poor quality tools.

 

[Fr J Hackett]

Thanks, did not know that, I do have one inaccurate steel set square. The other inaccurate ones are wood / brass assemblies for wood working. The Engineers Square is certified as right angle to some British Standard. I tested my set squares from collage draughting days against it and they are all accurate, so it really is just poor quality tools.

The easiest way to test a square is to use it to scribe a line then reverse the square and see if the edge and the previous scribed line are parallel.

 

[LadyInBed]

Dont trust squares bought from modern franchise tool shops and DIY stores, even branded quality items are not a right angle with many running off by 1mm over 6''. I bought a calibrated Engineers Square and tested a few I had at home and all were not true.

Make your own - 3x4x5 triangle

 

[savageseadog]

I think hole cutters are generally very slightly undersized from nominal. It's to allow for overcut in most materials.

 

[AntarcticPilot]

Make your own - 3x4x5 triangle

As used by the builders of the Pyramids! Provides a perfect right angle, and can easily be implemented with a bit of string.

 

[savageseadog]

I think hole cutters are generally very slightly undersized from nominal. It's to allow for overcut in most materials.

I've checked a few of mine, various good makes, Starret, Morse etc and they can be up to 0.5mm less than nominal although some are spot on. I measured mine across the teeth rather than the shank.

 

[KREW2]

I've checked a few of mine, various good makes, Starret, Morse etc and they can be up to 0.5mm less than nominal although some are spot on. I measured mine across the teeth rather than the shank.

Thanks for all the tips

Well I certainly caused a lot of head scratching at, at both Tool station, and Screwfix
I measured the 28ml one, and it cuts a 28ml hole.

I now have 3 x 25ml hole cutters the smallest cuts 23.6 the largest does 24.3ml. No good if you want to push a 25ml axle through

As suggested I splayed out the teeth, then finished with a round file, and the jobs a goodn, but it seemed a lot of unnecessary work when all I wanted was a 25ml hole.

 

[macd]

all I wanted was a 25ml hole.

Perhaps an imperial hole saw would give you what you wanted...say 1 cu.in.?
(Should you find a solution to your errant hole-saws, suggest you apply it to your predicative text, too.)