Drilling accuracy question.

[Michael GilliganParticipant @michaelgilligan61133]

Even betterer 🙂

MichaelG.

[Neil LickfoldParticipant @neillickfold44316]

Jason, Did you do every 2nd hole 1st time around, then drill in the middle of those 2 creating the open loop? As an apprentice had an exercise of cutting out the centre section of a large sheet, 30mm thick too big to fit the bandsaw. Was done with 5mm drills every second hole and with 5.1mm drill in between. It was later finished on one of the big mills. The inner piece was used to make another part of the project. Drilled on a large radial arm drill.

Very nicely done. Especially your drill sharpening.

[JasonBModerator @jasonb]

No I just worked my way round 1-2-3-etc with the Stub length then back to the start with the jobber.

Mr Dormer took care of the sharpening, though as I said getting a little dull.

 

[gerry maddenParticipant @gerrymadden53711]

The trial is done! This is what I did and learned (…or is it learnt?).

With the block carefully squared up, I measured the deviations of the spindle from the vertical. The latter was only significant in the Y-plane, in the order of 150um or 6thou over 100mm. I decided I would make a crude compensation for this by simply putting a shim under the workpiece at one end to align it better with the actual drill axis.

For the first 3 holes I used a spotting drill, a jobber, then the long YG. For the second 3 holes, I just used the spotting drill and then attacked the workpiece directly with the 8.1mm dia. YG. I ran at 500 RPM. The drill cut very good quality holes until I had to started to get into the ‘serious pecking’ range. Although chip compaction tended to change the surface quality of the holes, it wasn’t enough to open up the diameter measurably.

For the first 50mm of depth I found that the YG drill managed quite well to clear its own chips. By 75mm I had to help the process along. Winding the head up and down was a pain but I discovered that just raising the quill the full way (50mm) and clearing the higher reaches of the flutes with a hoover was quite satisfactory. However, as many predicted, that last 25mm became exponentially challenging. I had to wind up the head, and quill for almost every 1 or 2mm of depth cut. Quite tedious!

I suppose each 100mm deep hole took about 20~30 minutes to complete but I wasn’t really in any rush.

After a clean-up and a light debur of the holes, I popped in the 5/16AN bolts. To my complete surprise the bolts went all the way through from either end without any hint of snagging or tightness.

 

I then set about measuring, with digital callipers, the deviations of the entry and exit holes with respect to my two reference faces C and A as per the sketch above. The results are shown below:

I have to say I’m pretty pleased with this. It’s much much better than I anticipated. I expected over 1mm, perhaps even 2mm of wander, but to get no more than 0.64mm suits me fine.

I wonder though if these results could have been even better. If you look at the deviations from face ‘C’ on holes 1, 2 and 3, the figures are quite high compared with all others. These were the holes where I didn’t use the jobber drill between the spotting drill and the long YG. But these was also a little ‘issue’ that occurred during the process which I think was more likely to have been the cause of these relatively high figures. The block was sitting on a wide ‘parallel’ whilst clamped to the face plate, the idea being that I could move the parallel out of the way at the appropriate time to let the drill break through. At some point during the drilling of these 3 particular holes I noticed that the parallel had been quietly walking out of position from the cutting vibration. I tried to push it back with fingers under, only to discover it wasn’t at all keen to return to its initial position. Unfortunately, I had to resort to the use of a hammer. This strongly suggests that the block had in fact dropped a little, despite my very positive clamping of the block against my angle plate. Next time I’ll keep it in place with some plasticine.

Hope this is of interest and further encouragement to drill deep holes when you need to.

Gerry

 

 

 

 

 

 

 

 

[Michael GilliganParticipant @michaelgilligan61133]

Well done, Gerry !

MichaelG.

[EmgeeParticipant @emgee]

Gerry

An excellent result.

 

Emgee

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