Drilling on the diagonal?

[astro_al]

Hi guys, I need to weld some vertical bars (16mm diameter) into a frame which is tilted 25 degrees from horizontal. I want the holes to be a reasonably tight fit, so no oversize holes & fill with weld.

What is the best way to drill the frame on the diagonal so the bars slot in at the correct angle. The frame is 40 x 10 flat.

I've done a piccy to explain. I know I could drill it straight and die-grind the hole to suit, but where's the fun in that? I have about 60 holes to do.

Anyone know if mag drill broaching cutters don't mind one side biting first? Or perhaps I should use a milling cutter? I figure anything with a pilot drill is out.

Cheers, Al.

 

[GrahamGKD]

Al,
What if you were to make a sleeve for the drill, grind the one end of the sleeve at the appropriate angle and weld this to a plate. You can then drill though the plate to complete the jig. Clamp the plate part of the jig to the work and use the sleeve as a guide for the drill to stop the 'uphill' end of the drill being pushed off centre when it starts to bite? I'm not sure this would work but it is what I would try first, I think. Clearly there would be some wear on the jig, you may need to make several for your 60 holes, I'm not sure.
Graham.

 

[Ian B]

Mag drill cutters are perfectly happy when only taking a partial cut, and will work fine here, but with one big IF:

The rigidity of the machine that you're using has to be sufficient, and the work has to be clamped down. A milling machine's the ideal. Having heard how much slop some of the Chaiwanese drills have in the quills, using one of those might end up in broken cutters. They can shatter in a fraction of a second (ask me how I know this...)

Graham's suggestion of a guide bush is a very good one if you don't have a milling machine.

Ian

 

[jugs]

Al,
What if you were to make a sleeve for the drill, grind the one end of the sleeve at the appropriate angle and weld this to a plate. You can then drill though the plate to complete the jig. Clamp the plate part of the jig to the work and use the sleeve as a guide for the drill to stop the 'uphill' end of the drill being pushed off centre when it starts to bite? I'm not sure this would work but it is what I would try first, I think. Clearly there would be some wear on the jig, you may need to make several for your 60 holes, I'm not sure.
Graham.

Al, this is the best way to go, but you need to alter your drill bit, abit

The std drill point angle of 118 against your 25 gives you a huge sideways force, which together with the vibration from interupted cutting will shake the jig out of position.

The 16mm drill needs to be steeper say about 90, but at that angle the center 1/3 of the drill won't cut, so make a 16mm OD 8mm ID sleeve to pop into jig so you can drill an 8mm pilot hole and then the 16mm will be self-suporting almost straight away.

Try speeds about 600ish for 8mm & 250ish for 16mm with steady light feed. Use plenty of heavy oil/grease, & beware of snatch on breakthro.

Good luck.

 

[Hitch]

Broaching cutter would be ideal, no trouble.
As Ian mentioned, you need to clamp the bar nice and tight though.
Idealy you need a support just to the side of the hole, or you will bend the bar...i expect you know that anyway
.

 

[astro_al]

I'm dragging this back up.

I bought a mag drill arbor for my pillar drill. Works fine.

I bought a 16mm mag drill - used.

No dice.

No matter how hard I push / what speed I used, it just about scrapes the top surface of millscale away after about 30 seconds. I used coolant. It was rigid.

So - to business:

1. How do I tell if a mag drill / broach is blunt?
2. Are mag drill speeds the same as regular drill speeds for a given diameter?
3. Why is there a captive sprung ball bearing at the end of the bore of the mag drill arbor?
4. What are mag drill pins for? I see no way to use them on my arbor - is a mag drill different?
5. What do you reckon - is my cutter blunt, or what could be wrong?

Many thanks for any thoughts, Al.

 

[wyn]

The cutter should have chewed straight through...sounds like it must be blunt.

The cutter speeds would be similar to drilling/ hole cutting speeds. What really winds me up is people using mag drills flat out with large diameter cutters.

The ball bearing pushes on the pilot pin to eject the cut out "plug" from the cutter once you have gone through the bit of steel.

The pins fit down the centre of the cutter...there are various sizes...so it may not fit or might fall through.

 

[Endacy]

You get long or short cutters, and long or short pins. The pin goes through the hole in the cutter from the back, then you put the cutter into the arbor, the ball bearing you refer to has a spring behind it to push on the pin. As you progress through the workpiece the pin is pushed into the arbor out of the way. The pin is to centre the cutter to you punch mark.

Speeds, see here

Sounds like it's blunt - my ones cut like a hot knife through butter in steel.

 

[astro_al]

Thanks guys, I have ordered a shiny new one (plus a pin). I expect you're right.

Great chart by the way - ta.

Al.

 

[Wozzaaah]

Al, not sure where you ordered it from but just for future reference, Diy welding on here sells them at about the cheapest I've seen. All cutters include a pilot pin too where others charge for them.
They're cracking quality too, most of the ones I bought were genuine Rotobroach, ALL were made in good old Sheffield.

 

[astro_al]

Hi, thanks guys - it was blunt. Some moronic ebayer saying it was 'little used' - I should have known better...

I replaced it with a Unibor one from 'NEPUK SALES' on ebay - cost 11.14 with a pilot pin, delivered. Pretty good I think - also made in Sheffield, which is cool.

I tried a cut on the diagonal as a test - here is the result (16mm bar into 16mm hole - just fits in perfect, about 25 or 30 degrees (I didn't bother checking)). Bang on. Thanks, Al.

 

[Shox Dr]

I surprised you even thought about, a 2nd hand one, as they are so cheap.

Glad to see it finally worked out

 

[astro_al]

Me too... But, for a quid or so, I figured what the hell...

(cheapskate in denial).

Al.

 

[Shox Dr]

Me too... But, for a quid or so, I figured what the hell...

(cheapskate in denial).

Al.

I can't blame you there