Drilling & tapping

[Mick Annick]

Apologies for such basic questions, but it’s over 40 years since I last did any of this.

Need to drill some holes and tap to 10mm x 40mm deep into the end of 25mm solid bar. I drilled 3mm pilot holes first, then tried to enlarge to 6mm, but snapped 3 6mm drills in the process! What am I doing wrong? Drill speed too slow, too fast, wrong angle (I’m having to use a hand held electric drill)?

I eventually managed to get all the bits out and holes enlarged to 8.5mm for tapping, used a taper and then plug tap (1.5 pitch) , cleaned out all the swarf but the bolts don’t want to go all the way home, they screw in OK to about 25mm but then start chewing the thread. I’ve compared them to the taps and they appear identical (mesh with no gaps), I found a couple of old Nuts and bolts in my toolbox which screwed in fine, and the new bolts fit the old nuts OK, so I’m a bit baffled, what am I missing?

 

[gordon stephenson]

I would have drilled the 3mm pilot then straight to the tapping size drill. If the bolt is not going deep enough, maybe your plug tap is not sharp and does have a slight taper, You could try grinding a little from the bottom of the tap to ensure the threads go right to the end.

 

[Paul.]

I use spiral flute taps for blind holes, the spiral pulls the swarf out of the hole, use it by hand so that you can feel the thread being cut, and use a decent cutting oil such as Rocol RTD or similar.

 

[Mick Annick]

The taps are new from Tracy tools, don’t have any cutting oil so using Castrol Magnatec...

I flushed the holes out with 3in1 aerosol oil

 

[Kram]

Why 40mm deep, it wont gain much after 4-6 threads engaged, 10mm is fine.

This has saved me breaking a few drills
www.presto-tools.co.uk/file.php?filename=PrestoCounsellor2016.pdf

 

[jsf55]

Get some cutting fluid it will make all the difference, oil or paste

 

[Mick Annick]

Why 40mm deep, it wont gain much after 4-6 threads engaged, 10mm is fine.

This has saved me breaking a few drills
www.presto-tools.co.uk/file.php?filename=PrestoCounsellor2016.pdf

Thanks Kram, that’s really useful

 

[123hotchef]

what r u making

 

[Mick Annick]

Why 40mm deep, it wont gain much after 4-6 threads engaged, 10mm is fine.

That’s a fair point, how do you calculate the length needed for a bolted assembly?

Sadly the reason for the bolt in the first place is my poor welding ability - I’m trying to secure some gate posts to a frame that will be sunk in concrete, posts are three-legged 25mm solid bar, plan is to bolt them in place, shim if needed to get them trued up then weld to the baseplate, I’m just not confident of my welds alone holding them - gates are about 60kgs.

 

[Mick Annick]

what r u making

Gate posts, will put some photos up tomorrow

 

[Kram]

I have always been told it is four turns of engagement as a minimum which on 1.5mm pitch plus a chamfer is about 7.5mm, plus the taper length of your tap, but dont quote me on that it is always good to have extra, and Id say your 25mm threads will be plenty, if its the correct size bolt, a single m10 might not be enough for 60kg plus someone leaning on it. Im not able to imagine a 3 legged gate post so I will wait for the pictures

 

[slim_boy_fat]

@Mick Annick Did you reverse the drill every few turns to clear the cut metal from the tap thread? I've yet to attempt power tapping, although I have successfully used the lathe in 'manual' mode.

 

[Hopefuldave]

@Mick Annick Did you reverse the drill every few turns to clear the cut metal from the tap thread? I've yet to attempt power tapping, although I have successfully used the lathe in 'manual' mode.

I've just done a bunch of 1/2" BSF an inch deep in the lathe, spiral flute tap, Temaxol cutting goop, no stop-start - second lowest speed in back-gear (30ish RPM), turned out nice again

Dave H. (the other one)

 

[slim_boy_fat]

I've just done a bunch of 1/2" BSF an inch deep in the lathe, spiral flute tap, Temaxol cutting goop, no stop-start - second lowest speed in back-gear (30ish RPM), turned out nice again

Dave H. (the other one)

Swapping to back gear isn't that easy on the Myford, also no gearbox so mucking about changing gears.
For all the tapping I do, it's quicker in manual styliee

 

[Hopefuldave]

Swapping to back gear isn't that easy on the Myford, also no gearbox so mucking about changing gears.
For all the tapping I do, it's quicker in manual styliee

I don't use the leadscrew with taps, just loosen off the tailstock clamp, feed the tap in with the tailstock quill for a few turns then let the tailstock slide along the ways, tap pulls it quite happily!

How diffivult is it putting the Myford in backgear, isn't it just a pin and a lever or similar?

Dave H. (the other one)

 

[slim_boy_fat]

I don't use the leadscrew with taps, just loosen off the tailstock clamp, feed the tap in with the tailstock quill for a few turns then let the tailstock slide along the ways, tap pulls it quite happily!

Me too, but I have been turning both chuck & t/stock. Will def try that way.

How diffivult is it putting the Myford in backgear, isn't it just a pin and a lever or similar?

Nope, open a hinged 'hatch' in the headstock, and fiddle with a cut-down Allen key....

Dave H. (the other one)

 

[Rrobson]

You could have some compacted swarf in the bottom of the hole which is preventing you from tapping it right to the bottom. Get a pokey thing in to clear the bottom of the hole. Don't forget you'll have a chamfer on the tap which will reduce the tapped depth by a couple of mm.
Really surprised to get your breaking drills, can't say I've had this problem myself? Try a slightly bigger pilot and go straight up to tapping size. A bit of lube wouldn't go amiss either.

As for required hole depth, work on the principle of one and a half times the diameter of the fastener for maximum strength. Any deeper isn't going to make a huge difference.

 

[daleyd]

If your stuck for cutting fluid Toolstation or screwfix do wd40 cutting fluid in an aerosol - not bad actually - it was on offer at Toolstation the other day so I picked up a can to try.

 

[mike os]

For any tapping my rule of thumb is at least the major diameter, or nut thickness plus 1 turn (in steel)

 

[Brad93]

You are using a hand drill to drill the ends of round bar?

likely you’re not going in straight.

needs doing in a lathe really, would be a 2 minute operation.