Micro drilling problems

[DalboyParticipant @dalboy]

I am in the progress of drilling a part for the fuel mixer on the farm boy I am making. This requires a small cross hole of a #76 bit through a 1/” brass rod which has a centre drilled out and threaded.
What is the best way to do this. The first attempt failed and broke the bit after drilling through the first side.
So far I have lost one bit and broke two (I dropped the first and being the size it is never to be seen again, damn shop gremlins)

I am trying to do this in the mill. I know that you can make a sensitive drilling attachment for the lathe which I have but to set this up in that could be a problem due to the size

Any help appreciated

[bernard towersParticipant @bernardtowers37738]

Drill the hole before it has a hole through the centre, or drill halfway or less then rotate and drill halfway again. And I be surprised if your mill has the drill turning fast enough. Best of luck. Oh and another thing peck drilling stops the drill from getting clogged.

[roy entwistleParticipant @royentwistle24699]

I would do it through the rod with the centre hole in the rod before threading the hole

As Bernard says keep pecking and take your time

Roy

[JohnFParticipant @johnf59703]

Delllboy — look at your messages   John

 

[Peter Cook 6Participant @petercook6]

I use Arc-Euro’s Sensitive Adapter in the mill, running as fast as possible. I also find these Carbide drills work well on brass if you can find an appropriate size.

[Martin ConnellyParticipant @martinconnelly55370]

You need a very small feed per rev on these very small drills. If you do not have a very high RPM then controlling the feed rate with a basic drill is prone to issues as the slightest jerkiness of feed can bust the drill bit. The sensitive drills are used by many people because you can feel the pressure being applied to the workpiece. The leverage and gearing found on manual drills and mills takes away that feel. I would expect the maximum feed per rev for a drill of this size to be about 0.0065mm or 0.00025″ so that works out at 6.5mm/minute or 0.25″/per minute per 1000rpm. So if you are limited to say 3000rpm you are limited to a feed rate of 19.5mm/minute or 0.75″ per minute. This is very slow and also hard to control manually, as I said a slight jerk will take you beyond these feed rates very quickly and you will not feel the pressure build up that will break the drill. It is hard to manually control a large machine with such care as is needed here (unless using a power feed or CNC in MDE mode).

Martin C

[DalboyParticipant @dalboy]

Thank you everyone, I think that I have solved the problem by reading the answers here and on another forum.

Just clear up a couple of points which I forgot to mention’

1 I am using a jig to keep the drill bit in line

2 yes, I have been pecking at the work to clear the swarf from the bit

3 I am drilling at a fast speed (as fast as I can on the milling machine.

Now for the reason I think that I have been having which is so simple, but until someone mentioned it I missed.

And that was, I am trying to drill right through with a thread in the hole I am trying to cross drill and the thread is causing the bit to wander off course and breaking the bit.

I will try again with the remaining two #76 bits wish me luck

And thank you again for all the help gents

[JasonBModerator @jasonb]

If you can then drill the small hole first as doing it after will mean as you start the opposite side the drill bit will be deflected by the angle of th ethread.

You could come at it from both sides but even then have an uneven exit.

If you have  alot of work in teh part then maybe screw a piece of brass into the threaded hole to support th edrill on exit and entry.

No need for a jig, tiny spot drill to start then just drill it.

[Speedy Builder5Participant @speedybuilder5]

Drill a larger hole then (in the lathe ) make 2 small bushes to go into the hole ?? Push the bushes into place with a lactate sort of product.

if you can’t win – cheat !

[Speedy Builder5Participant @speedybuilder5]

Spell check alert!  Loctite, Loctite.  Where was AI  when you wanted it.

[Michael GilliganParticipant @michaelgilligan61133]

Well caught, Sir !

MichaelG.

[ChrisLHParticipant @chrislh]

And I was thinking he was turning up a nipple to push it in with.

[Author]

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