You'd just raise the cutter, scrape the slug sideways with a screwdriver, and carry on...
Another thing is that a mag drill won't have much grip on 3mm steel so you would have to take your time.
Make a bunch of swing-over stops and set them onto a strip of plate alongside your drilling jig. Line them up spaced at the hole centres. Then all you have to do is feed your tube to a stop, drill, flip the stop and feed the tube to the next, drill and so on. Clamp a rotary stop to the tube to keep them all in line.
You should have asked sooner I have just thrown a bag of holes away
I agree if it's measured from one point.
My brain is failing to grasp how a fixed point can be more distance away if it's measured over a short distance.
Maybe I am being dense (not unknown recently) and now I have seen more info on lengths and number of holes etc I am agreeing with Brad. Laser would be best. But if I have an accurate pin that references/fits into an accurate hole ( bearing in mind we used a hyperthetical 0.01 error, which in reality is not likely to be achievable in reality) I drill a 20mm hole that would be accurate (as it's the first one).
Once the hole is drilled the bar is moved until the pin drops in.....let's assume a 0.01 error.
Then the same is done again...that still only gives a 0.01 error between the two holes. So as the tolerance was 0.5mm all of the distances between the holes are 0.01 and we'll within tolerance.
If all distances were measured from one fixed point and incurred an error of 0.01 I can see how the last hole could be 0.01 X the number of holes.
Over the last six months I’ve had a few smallish batches (40 x900 mm lengths) of 20x40 stainless box laser mitre cut.
it worked out about the same price to laser as each 900 mm piece of box cost.
I garentee it would be cheaper to laser it than stand there drilling holes
The distance between the two holes will never be worse than the error in the jig but the error from where the hole should be (That is, relative to a fixed reference, say an end) will be compounded every time you drill a new hole.
Say your jig is 40±0.1mm long and you need to achieve ±0.5mm, something bolting to a pair of adjacent holes will fit just fine but something which bolts to the holes at opposite ends could be as much as 5mm out, well outside of the tolerance.
If the OP wants to keep it in house a simple jig and plasma with a drag tip would do. Each hole would only take seconds, the MT4 rack I made below was done with a simple jig and plasma.
If you jig is out, plus clearance to locate adding to the error, the first holes is x (0.01 in your example) out. Second is x out from the first - so is 2x (0.02) out from the datum. Third hole is x from the second . ..3x out . . . etc.
If you have the same error "x" on measuring each hole from one fixed datum, each hole is only "x" out . . .
Just better practice - same idea applies when creating a drawing for such an item - although you will see notes such as "errors must not be cumulative" on drawings - when the better idea would have been to dimension it differently.
If you can drill to 0.01 without a milling machine you can do my drilling
I have to admit to being amused by the first post "very accurate" . . . and then defined later as "0.5" That's carpenters accuracy with a cloth tape with one eye shut and a thick pencil in the dark
As others have said - farm it out to someone set up to do it - by the time you've knackered numerous hole cutters, wrecked the pillar drill, realised your "0.5" is now 10mm at one end on one side, the holes on another side are in a nice curve, and the holes on the other side don't line up . . . on the first one . . .
id clamp the tube to a board with a backstop and end stop that way you keep the orientation and you will then have a repeatable distance to the centre of the tube.
along the line of the backstop i would pencil mark you hole locations the align that to a pointer on the pillar drill worktable which will also be your you stop, should easily manage 0.5mm
@rory1, would you mind sharing where you had your laser cutting done? Iv've contacted a few places but no responses yet. Thanks.
Ah ah well I was going on the fact the OP said he needed evenly spaced holes.
That's why I said the sizes were unlikely to be achieved in the real world using my method.
Ok I agree when you write it like that.
It really does depend on what it's being used for.
Hey you must have thrown them over here, after forgetting to empty some washers out my trouser pocket before washing my wife found a pile of “holes” in the bottom of the washing machine.
Mellards, stoke on Trent
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