Reasonably accurate holes in box section

[grim_d]

Gents,

I need to punch 120 "20mm" holes right through 3mm box section to take 20mm ERW round tube. Id like a fairly good fit so they don't sag too much (they are for panel drying racks). They are not being welded in to remain removable if I need more space above a rack All the tubes are fairly consistent at 19.98 - 20.08mm.

tried some cheap hole cutters but the holes end up closer to 21mm which I'm not happy with.

What's best to use here? Annular cutter? I don't have a mag drill but I can make an arbor easily enough and use it in pillar drill, the runout from which might give me just enough clearance...I can always shave the ends of the tubes in the lathe if necessary (but id rather not!)

The box section is too long for me to get it in the mill.

Thoughts?

 

[PhillipM]

Step drill, but it'll take you a while.

 

[Barking Mat]

Step drill, but it'll take you a while.

And probably a few step drills.

 

[grim_d]

Step drill, but it'll take you a while.

If only they did ones with 51/64th step on it.

To be honest it works pretty well apart from having to shave down 120 tubes....and the cost of step drills.

 

[Tigman]

Rotabroach do an annular cutter that fits a Jacob's Chuck , if you have a pillar drill !

 

[Kram]

What sort of hole cutters? The hydrualic or bolted punch type?

 

[DAPPH]

Can you not hire the mag drill and buy the broach ?

 

[grim_d]

Rotabroach do an annular cutter that fits a Jacob's Chuck , if you have a pillar drill !

I have 3 pillar drills

What sort of hole cutters? The hydrualic or bolted punch type?

I think "hole saw" would be a more accurate term....and ones from Rennie at that.

Can you not hire the mag drill and buy the broach ?

at £90+ per day...it's not my first choice.

 

[addjunkie]

Would be a rotorbroach for me

 

[PhillipM]

And probably a few step drills.

Nah I do this day in, day out with box section, sometimes it's your only option, usually get 400-500 holes out of one good un.

Rotabroach is better but you'll be surprised how well a step drill holds tolerance in a pillar drill I'd imagine. All my fittings end up a light tap fit size-on-size until the drill just won't cut any more.

 

[Tigman]

I do this on 50 x 50 box with rotabroach cutter just like a hole saw , the pilot drill pierces the underside of the box , have to turn it over to drill that side
Plenty of cutting oil

 

[Munkul]

Expensive option, but fast and accurate, would be a HMT turbo drill. As long as you use lube, you'd get a good long lifetime out of it, similar to a stepdrill really.

 

[grim_d]

Nah I do this day in, day out with box section, sometimes it's your only option, usually get 400-500 holes out of one good un.

Rotabroach is better but you'll be surprised how well a step drill holds tolerance in a pillar drill I'd imagine. All my fittings end up a light tap fit size-on-size until the drill just won't cut any more.

That's an incredible amount of holes from one cutter, I suppose I've technically got 240 to do, may I ask what ones you use?

 

[Kram]

I think "hole saw" would be a more accurate term....and ones from Rennie at that.

Got a picture? If its just a hole saw you can grind the OD down to the size needed.

I had a 16mm holesaw that did a poor job and had far too many teeth, many teeth chipped. I ground it back to make a 2 tooth cutter and worked perfectly.

 

[grim_d]

Got a picture? If its just a hole saw you can grind the OD down to the size needed.

I had a 16mm holesaw that did a poor job and had far too many teeth, many teeth chipped. I ground it back to make a 2 tooth cutter and worked perfectly.

Just your standard hole saws. They are really cheap nasty ones though, the 20mm one has a OD of anywhere between 19.1 and 20mm on the same cutter, more like an egg than a circle. It's not that its too big, its too rubbish

 

[Tigman]

Versadrive do a nice tct cutter for chuck as well

 

[PhillipM]

I do this on 50 x 50 box with rotabroach cutter just like a hole saw , the pilot drill pierces the underside of the box , have to turn it over to drill that side
Plenty of cutting oil

That's what I do, use the pilot from one side to start the other, works well enough for most stuff.

That's an incredible amount of holes from one cutter, I suppose I've technically got 240 to do, may I ask what ones you use?

TiN ones from drill-service - little pricey, mind.

 

[DAPPH]

I have 3 pillar drills



I think "hole saw" would be a more accurate term....and ones from Rennie at that.



at £90+ per day...it's not my first choice.

I saw Ayrshire .......after I'd posted .

 

[owas]

Get it laser cut

 

[grim_d]

I saw Ayrshire .......after I'd posted .

Not sure what that means but either way it's probably true.

Get it laser cut

Calm down!