Model Engine Maker
Help! => Mistakes, muckups, and dangerous behaviour => Topic started by: Sky King on March 31, 2019, 03:51:38 PM
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In the process of building Elmer's #29 Mine Engine and had gotten down to the cylinder and drilling all of the 19 holes required.
Well, all went just fine until the last hole,one of the steam passages, had only a few thou to go and "ting"!!! @#%^&%#@ bit broke!! Tried every trick in the book and never could get it to budge. Beat it up so bad I just threw it in the mistake drawer and started a new one. This time I drilled the passage holes first!!
Yes I was "peck" drilling,,only about 20-25 thou at a time...
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Did you spot drill?
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Yep, and even milled a 1/16" starter hole about .125" deep to keep bit from wondering out due to the angle.
It was very close to being all the way thru when it broke. Left about 3/32" piece..
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What were you making the cylinder out of?
Tony
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Adding oil between 'pecks' helps. Might just have been a dull bit?
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It always seems to be that LAST hole. One of Murphy's corolaries no doubt.
Bill
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Aluminum
Bit could have been dull
Been around a while
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For me it usually starts with a dull bit. Since it’s dull it tends to wander. When the wander gets big enough the side loads cause the bit to go tink. It’s amazing how well you can diagnose it after it happens but never see the signs when your actually working on the part.
Tony
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Drop of cutting oil, especially for deep holes, and frequent pull-outs to clear ALL chips and brush on a little more oil, makes a big difference. Sharp drills are always better, of course.
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If the cylinder is aluminum (or other non-ferrous material), you can use a saturated alum solution to dissolve the broken drill fragment.
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Sorry to hear about the broken bit. I can relate to the "last hole" thing... :(
Kim
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Actually that is the first bit I have broken in a really long time,,
Can’t say that for taps!!!
Never thought of the alum,, will give it a try and might be able to salvage something for another day
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Been there done that, more than once. :-[
When drilling and milling aluminium alloys I use a squirt of WD40. It stops the chips "welding" to the cutting edges but allows the chips to be thrown clear of the flutes when the tool is retracted. The trouble with oil is that it is sticky so the chips tend to remain in the flutes. Was it a quality drill? You can bend a HSS drill a fair way before it breaks. I didn't extract a drill properly on the CNC mill before the table set off to the next hole. The drill must have bent at least 20° but it didn't break. Carbide is different, a bit off and it snaps.
Andrew
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I don't think it broke due to side load or bending. I think it seized and twisted into,,,just guessing~!!!
But I will use every one of everyond's suggestions in the future!!!!