don't want to ruin a 3rd gearbox mount 
went to drill a hole, brand new drill bit (thankfully slightly undersize) and somehow ended up with a triangular hole?!
bolt fits alright, still quite snug, but why did that happen? is my actual drill knackered?
Description
[Edited on 13/5/10 by blakep82]
Looks to me that you had the drill running far too fast , then let it flap about a bit............
that happens to me in softer materials too! What kind of drill did you use? Might be a due to some play on the shaft (like more on yours so it happens with steel too) But is it really a problem? As long as the center of the hole is on the right spot, you should be alright with tightening it a little more than usual?
n00b
Sounds like either the bit was not in the chuck right, or bent bit, or bad bearings in the drill, or too high of drill speed. Was it a hand drill or drill press? Russ
All drilled holes tend to be slightly triangular. It's just more pronounced at larger sizes and even worse if your drill has a bit of play in the chuck and/or bearings.
it was the slowest the drill would go.. it works in this case, but i didn't want to ruin the other hole on the other side... i'l try and
charge my battery drill, thats got variable speeds. my mains power one only has 2 speeds.
not sure what type of drill tbh, hss maybe?
wonder if there was a bit of something in the chuck, so the drill didn't sit right? i'll have to take it apart and clean it out
quote:
Originally posted by cd.thomson
n00b
Drills do that! if you want a perfectly round hole start much smaller than you want the hole then gradually increase drill size about a millimeter at
a time remembering the bigger the drill the slower the speed required. Watch for the swarf coming off the bigger the bits the better otherwise you are
grinding rather than drilling!. Also make sure drills are sharp and clean. Slow and steady!
Caber
quote:
Originally posted by blakep82
quote:
Originally posted by cd.thomson
n00b
correct. i don't do drilling. i always f*** it up somehow... taken to getting most stuff water/laser cut
quote:
Originally posted by cd.thomson
quote:
Originally posted by blakep82
quote:
Originally posted by cd.thomson
n00b
correct. i don't do drilling. i always f*** it up somehow... taken to getting most stuff water/laser cut
im only messing bud, its the beer talking.
brothers 18th tonight
will do the other one once i can get under the car. its easier that way to get the hole in the right place
hes in bed!! 
dont make em like they used to
quote:Yes. this.
Originally posted by Richard Quinn
All drilled holes tend to be slightly triangular. It's just more pronounced at larger sizes and even worse if your drill has a bit of play in the chuck and/or bearings.
Hand held power drills are crap for drilling accurate large holes in metal IME. They are too fast and too uncontrollable. You really need a nice slow bench or pillar drill with a proper vice so everything is held rigid.
The drill bit and workpiece were moving relative to each other so the drill bit was able to "wobble" about in the hole.
If it's a pillar drill, clamp the piece down harder, if this doesn't work then you're probably got play in the bearings (my cheap
pillar drill can do this)
If you want to minise the effect, try starting with a small pilot hole and gradually work up the bits 1-2mm at a time
quote:
Originally posted by blakep82
... taken to getting most stuff water/laser cut
quote:
Originally posted by cd.thomson
hes in bed!!
dont make em like they used to
This can be due to a number of reasons:
It is called Tri-loballing.
It is caused by instability
Reasons for tri-loballing:
Incorrect Speed and/or Feed.
Drill too long for job in hand.
Pre-drilled hole.
You should always drill into solid material.
Drilling into pre-drilled holes removes the self centring properties of a drill. This is called Core Drilling and you 'should' use a drill
specifically designed for this purpose. You can usually get away with it though you do get snatching and Bell Mouthing - occasionally the drill will
split right up the middle due to torque.
The reason it happens is very similar to a Rotary Engine - if the drill had 3 flutes it would cut a Square. The drill needs centre support!
When drilling thin material - to prevent triloballing , use a steel block underneath. Keep the Drill as short as necessary. Drill through the plate
into the block and it will prevent this. If it does not you will find that the Web (Centre Chisel Point) of the drill is too thick and causing
wandering. Thin it down if you can using a grinding wheel.
Hope this helps!
I posted details about this years ago - try searching for "Drill Geometry"
EDIT - Drill Information
Steve
[Edited on 13-5-10 by Hellfire]
To big and to fast.
start with a pilot hole and go bigger a few mm at a time.
My Dad, a machine fitter by trade, said they always drilled 1/16" under size and reamed the hole to the final diameter. Perfect round holes every time. Then they demolished the entire factory and it didn't matter any more.
Quick trick to stop this...
Put a piece of emery cloth grit down on where you are drilling the hole then drill through the cloth and the work.
Voila - one round hole...i kid you not!
This is normal on thin sheet with jobber drills anyway and nothing you did wrong. Its mostly down to lack of support for the tip of the drill as it
breaks through meaning you get some movement between the work and drill.
David
If you are hand drilling you could always try a step drill.
They seem to leave rounder holes.
You are limited to about 2.5 - 3mm metal thickness due to the step (double that if you can get to both sides of the hole).
quote:
Originally posted by minitici
If you are hand drilling you could always try a step drill.
They seem to leave rounder holes.
You are limited to about 2.5 - 3mm metal thickness due to the step (double that if you can get to both sides of the hole).
, better using a bench drill if you have
one when using a step drill and clamping it all down.. My 30Quid bench drill is very useful if totally accurate (some bearing run out) for bit's
like that. All drills make 'sided' holes where the number of sides is one more than the number of flutes on the drill. Its more pronounced if the drill
can wobble eg hand held drill or nacked bearings in a press. You can make a 'wobble chuck' so that you can deliberately drill
triangular/square/hex holes with the appropriate drill.
Regards
Hugh
quote:
Originally posted by hughpinder
All drills make 'sided' holes where the number of sides is one more than the number of flutes on the drill. Its more pronounced if the drill can wobble eg hand held drill or nacked bearings in a press. You can make a 'wobble chuck' so that you can deliberately drill triangular/square/hex holes with the appropriate drill.
Regards
Hugh
Plenty of video's on youtube showing the drilling of square holes if you're interested.