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A First for me

Garno

Garno

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May 12, 2021
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Dronfield
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Gary
Both a first followed by another chuffin mis-hap (nothing new there)

First off I was drilling a hole in a brittle bit of acrylic and next thing it just broke up, I say broke up but exploded is nearer the mark. 12.5mm hole.
This has never happened to me before and I am glad I was wearing a full face shield as at least 2 chunks hit it, scared the life out of me when it happened. I discovered something when it blew and that is that fat, bald old blokes can move fast at times.
The only thing I can think of is that the speed of the lathe was going too fast (I do all my drilling on a lathe) and built up some heat, although drilling a longer hole with a 10.5mm drill bit at the same speed and with the same blank caused no problems :thinks:

Next to the mis-hap, another blow out, this time whilst turning, right at the finishing part as well. 12.5mm hole using some red, blue and white ply.
That is twice I have had mis-haps using ply, both following on from each other.
Only thing I can think of here is that maybe the chisels are not sharp enough, I am basing that on nothing less than a stab in the dark :whistling:
 
A

AllenN

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May 20, 2013
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Lancaster, UK
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Allen
Couple of thoughts. When drilling acrylic I find slow speed and a gentle touch best. You have to let the drill bit actually cut not try to bully it’s way through. I am assuming that the drill bit was sharp by the way. A couple of mm on the diameter does mean quite a large increase in the peripheral speed at the outer edge of the drillbit. I haven’t calculated it but it might be the difference between just getting away with it and failure. What did it sound like? Sound can often tell you whether something is cutting well or really being forced through.
With ply, remember that the grain in each ply is going in different directions so you are repeatedly hitting end grain even when you might not think so. Very sharp tools and a gentle shearing cut would be my preference.
+1 for the face shield, it may make us look like an astronaut but I for one would rather keep myself I one piece for as long as possible.
 
Dalboy

Dalboy

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Mar 20, 2014
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Kent
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Derek
Never drill all the way through an acrylic blank slow speed and extract often to clear the chipping. I always have a blank at least 5 to 10mm longer drill most of the way through leaving at least 5mm and stop then chop off the last bit which leaves a nice clean hole. Allowing heat to build up will normally end up with a hole oversize as well as a possibility of it running off centre.
 
Terry Q

Terry Q

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Oct 8, 2014
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Roanoke, Illinois USA
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Terry
Derek nailed it for acrylics, slow feed rate and clear the swarf often. I had the same problem with plywood blanks. My solution was to stabilize them. If you get a chance to try a stabilized blank i'm sure you will like it.
 
TVS

TVS

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Nov 21, 2021
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Notts
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Woody
Sounds to me like the material was cast polyester not your standard acrylic which only needs to be touched in the wrong way and bang game over as has been suggested slow speed for drilling and fine cuts when turning takes a bit of getting used to
 
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