20mm hole drilling - mag drill cutter?

[Hitch]

Upto about 12mm, id just go with whatever is too hand normally though.
as gav says, if you use steps that are close together, it will snatch easily. Not much of a problem on a small bit, but 20mm running at slow speed has more grip than most hands

 

[astro_al]

Right, yes point taken on the torque thing.

I need a bigger table on my drill anyway - had to support half the piece on a forklift next to the drill the other day, hardly ideal!

Anyone got a nice geared radial arm drill they don't want?

Al.

 

[gavuk]

only other trick is if you are clamping work down .i set up by reversing the drill direction to centre work,clamp tight ,then go forward to drill(obviously)

 

[snowcat]

I wouldnn't go bigger than 10mm for a 20mm hole nomally i go just larger than the chisel centre of the final drill......if u go 16-18mm it will be more difficult than leaving more meat .....more tendency to snag ,i'm sure others will may have a different opinon ,works for me ....Gav

No Gav your quite right, a pilot is only really to center the drill up, too big, it will snatch as you say and also vibrate, even when working some of the 3-4" drills I will still only pilot with a 13mm bit, as long as the powers there your best to let the faces do the job there intended for... small cuts are what a reamers for

 

[Pete.]

Pilot at 1/3 diameter then put the big drill in. I'd use a mag drill and annular cutter myself, and loads of cutting oil. That's what we use at work.

 

[Blackjack]

Right, yes point taken on the torque thing.

I need a bigger table on my drill anyway - had to support half the piece on a forklift next to the drill the other day, hardly ideal!

Anyone got a nice geared radial arm drill they don't want?

Al.

Dunno about don't want, but....

 

[mgarym]

Is there a chart for drill speed settings for different size drills
and material thickness and type?

 

[astro_al]

mgarym - get a 'zeus book' (ebay / google). Cheap and handy!

Blackjack - a fiver enough?

Al.

 

[Weldingartisan]

As you have a lathe, buy a morse taper blank for around a tenner and make your own broach holder - by far the easiest way, no pilot hole and cuts faster than a twist drill with no 'snatch' on breakthrough.W/A

 

[Tigman]

I have a Rotabroach drill great bit of kit , the only thing missing would be the spring loaded centre this pushes the slug out as the cutter goes through , the centre also aids the start , stops the wandering if that makes sense !

 

[Blackjack]

Blackjack - a fiver enough?

Al.

No?

 

[mgarym]

Thanks astro i'll look into getting one
i suppose it does drill/tap sizes also

 

[Blackjack]

Thanks astro i'll look into getting one
i suppose it does drill/tap sizes also

Yeah it does, but...

thread size minus pitch = drill size for metric stuff.

So...

8mm x 1.25mm thread, 8 - 1.25 = 6.75, you only use the first decimal place, so that's a 6.7mm drill.

10mm x 1.5mm, 10 - 1.5 = 8.5mm drill.

Saves looking it up.

 

[mgarym]

thats handy to know thanks