Drilling counterweight?

[The Mekon]

I have a question that may appear a bit simple -but here goes.

My EQ6 mount has a special counterweight shaft that was machined up to be 24mm diameter. My vernier measures it at 23.97mm

Now I want to buy a smaller EQ3 counterweight (19mm hole) and then drill it out.

Q. If I order a 24mm drill, can I be assured that it will drill out slightly larger than 24mm, or will it end up being an interference fit and I will struggle to get the weight on the shaft? If so I will have to order a 25mm drill.

many thanks

[brian nordstrom]

:thumbsup: John all drill bits drill slightly oversize , you will be fine with a 24mm drill , it will drill to about 24.10 or there about's .

Or take it to a machinist and get him to sharpen it so it drills a little bigger eg. one cutting edge slightly longer than the other . Do this after the first boring with the new bit .

Or for the price of a 24mm bit ( they ain't cheap ) you will use once , get a machinist to drill it out to 31/32 which is 24.61 mm .

Brian.

[LewisM]

Those Chinesium pot-metal counterweights are SOFT steel (probably dross from the top of the casting vessels :P) - they drill VERY VERY easily.

A drill press makes the job easier - mount in the drill press table vice, and go at it. I found didn't even have to lube the bit very often it is SO soft (simple 3-in-1 oil was fine as a cutting oil).

[The Mekon]

Thanks Brian, Lewis.

I think I will go for 24mm - I can buy the bit for just over $20 - my local machine shop charges $80 per hour in 15m increments, best to do it myself as I do have a proper drill press.

[Saturnine]

John

Be very carefull drilling out an 19mm hole to 24mm, the 24mm drill will bite in and grab the sides of the hole because the cutting edge doesn't have any support along most of its length, from the centre outwards. Because it doesn't have that support the drill will certainly wander and drill oversize, maybe by as much as 1.00mm.
It's good that you have a drill press, would be impossible otherwise unless you could put the counterweight in a lathe chuck and the drillbit in the tailstock . Another good idea is to take the sharp edge off the drill cutting edges so that they are less likely to bite and grab into softer metals, the method is called " brassing the drillbit "
I'm sure you will but make sure that the counterweight is well clamped in the vice or to the drill press table and the table clamp to column is tight, otherwise the setup could " chatter " and end up with an out of round hole.
Maybe I'm stating the obvious but as an now retired fitter & machinist I've had a bit of experience with this sort of work over the previous 45 years.

Good luck
Jeff

[miker]

John, drills are available in 0.1mm increments. You can buy a 24.1mm drill.

Michael.

[JA]

Hello M,

You'll be fine with a 24mm drill (in a drill press with the work well clamped), BUT it would be better if you had a friend with a lathe (and boring bar). Then there's no need for a 24mm drill and you could then tune for whatever degree of fit you prefer and add a chamfer to the hole to ease the fit to the shaft.

Best
JA