Magnetic ballpoint question

[qquake]

I just got some of the new (to me) Berea Magnetic Ballpoint kits from Turners Warehouse. It calls for a Letter V drill bit, which is .377". Any idea why they specified that instead of 3/8", which is .375"? Does .002" really make a difference? I drilled the blank with a 3/8" bit first, then "chased" it with a Letter V. The V didn't cut anything from the blank at all.

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[magpens]

I don't have an answer. . Similar call for a "V" with other kits. . Same question ... "Why not a 3/8" drill ?"

If you actually measure a "V" drill, you may even find it is undersize from 0.377" ... that's what I found, even with high quality Norseman drill.
Maybe my calipers are "out", but I kinda doubt that because they are fairly new and well cared for.

 

[TonyL]

You can always go tighter and test the tube.

 

[Dehn0045]

actual hole diameter depends on material, tools/setup precision, and technique. Often I will drill two different blanks with the same exact setup and get different final hole diameter. My setup is far from perfect so I usually choose a bit that is closest to tube diameter, or 1 size small, and then use sandpaper to get the desired fit with the tube. This also allows for a slightly larger diameter at the ends, which I believe helps to prevent cracking when pressing in fittings.

 

[its_virgil]

If the hole from the 3/8 ths bit will allow the tube to clear then use it. If not, use the V or whatever bit will give the correct size hole for the tube. Personally, I never go by the drill bit choice on the instructions. I measure the tube and choose the best size. I always test drill on a scrap piece of material. Only Berea can answer why the V bit was specified, or the author of the instructions.
Do a good turn daily!
Don

 

[Charlie_W]

I usually measure the tube and then try to find a bit that is 0.010" larger. If painting both blank and tube, you may need a tad more room.

 

[qquake]

The 3/8" bit worked fine.