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prkaye

Well Known Member
Does one use the same countersink bit for #30 holes as for #40 holes? I think I only have the one countersink bit.
 
I have diffferent c/s bits.. 30, 40, 12.. needed 'em all at some point.

40 would wobble in a 30 hole (try it on a scrap piece!) and wouldn't give you a nice countersink.. you really would want (at least) one for each size needed.

the difference between them is in the pilot size.. external diameter is same.. having correct pilot size will ensure that it doesn't wobble in teh hole, giving you a nice countersink.
 
Get specific bits. On my 7A I've needed #30, #40, #12, #19, #28, #6 screw and #8 screw.

I would recommend 3 microstop countersinks to trade $ for quality and time. Set one up for #30, 1 for #40 and use the 3rd for all other sizes. Why, you will save lots of time by not changing back and forth between 30 and 40 plus, you can set them once for the 30 and 40 and keep a nice exact countersink - no more low or high rivets.

Jekyll
 
$$$$$$

prkaye said:
Does one use the same countersink bit for #30 holes as for #40 holes? I think I only have the one countersink bit.
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Not for long :eek: .......you are starting on the seemingly never ending tool acquisition path....Bob Avery has another convert - or whoever is your tool supplier of choice

I did as Jeykll recommends and ended up buying extra cages and setting each one up at the correct depth to save time..... :D

That reminds me, got to go and order another tool that I need for the Fuselage !!!!!!
 
Jekyll said:
I would recommend 3 microstop countersinks to trade $ for quality and time. Set one up for #30, 1 for #40 and use the 3rd for all other sizes. Why, you will save lots of time by not changing back and forth between 30 and 40 plus, you can set them once for the 30 and 40 and keep a nice exact countersink - no more low or high rivets.

Jekyll
Click to expand...

This is probably the number one tool improvement I would invest in if I were building all over again. Changing countersinks is a huge pain and timesink...why give yourself another reason to dread countersinking? :)

I think I saw some pretty cheap used countersink cages (for the less-commonly used sizes, ideally) at The Yard.
 
It's theoretically possible to get by without some of the larger sizes. You just need to drill the hole small first, then countersink, then enlarge the hole. For example, say you need to countersink a #12 hole and only have a #30 countersink. First drill to #30, countersink the hole, and then drill to #12. The big drawback (besides the time lost screwing around) is that it's difficult to know when you've countersunk to the correct depth. You can't fit a #12 screw into the #30 hole to test it.

Dave
 
Davepar said:
It's theoretically possible to get by without some of the larger sizes. You just need to drill the hole small first, then countersink, then enlarge the hole. For example, say you need to countersink a #12 hole and only have a #30 countersink. First drill to #30, countersink the hole, and then drill to #12. The big drawback (besides the time lost screwing around) is that it's difficult to know when you've countersunk to the correct depth. You can't fit a #12 screw into the #30 hole to test it.

Dave
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Dave:

This may work for you however, the cost of countersink bits is minor when compared to the cost of replacing parts due to errors using this swag method. Some parts are critical and expensive. I would not recommend this practice for the novice.

Jekyll
 
Agreed. I threw it out there as an alternative for the builder on a super tight budget, but countersinking is tough enough in ideal conditions. It's better to get the right tool for the job.
 
the numbers

I looked through my stuff on the weekend, and discovered I actually have 4 different countersink bits. Three of them are still in the packages and area labelled as follows:

1) COUNTERSINK BIT 1/8" -#6 SCREW
2) COUNTERSINK BIT 3/16"-#16 SCREW (think it says 16... smudged label)
3) COUNTERSINK BIT #21-#8 SCREW

I don't have the label for the other countersink bit, but engraved on the bit itself is the following text:

4) 1/2x100(degrees) .092 ACT

Could someone help me understand these different sizes? Questions:

A) Which bits should I use for countersinking #40 holes and which for countersinking #30 holes? What about other common hole sizes?

B) Can you determine the size of my countersink bit (4) above, based on what is written on the bit itself?

C) Do I need to get other sizes?

Thanks!
 
Use a #30 for a #30 hole, etc.
.094 is 3/32", just slightly smaller than #40 (.098"), maybe it's for 3/32 screws
 
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>> Use a #30 for a #30 hole, etc.

But if you look at the list of my bits on my post, I don't have any that are labelled as #30, or #40. They came as part of an RV toolkit from planetools.com, so I'm sure they must be one of the ones I have listed...

Perhaps the one labelled 1/8"-6 SCREW is for the #30 holes?

Perhaps the .092 is for the #40 holes?
 
A #6 screw actually measures about .136", so maybe they are trying to double-up with the #30 which measures .1285", just slightly bigger than 1/8"
 
I believe they are just combining some sizes, which probably won't hurt anything and are just trying to save you some money.
 
cool

Oh yeah, those are cheap. Think I'll pick up a few, and some microstops, as recommended by others.
Now, do I need 82-degree countersinks, or 100-degree countersinks??
 
Tools I needed

In the end I had 5 microstop tools for countersinking and rivet shaving. They were not used except where necessary but the right size was always used when countersinking was done. This is an error phone task. The three that were used most were the one for 3/32" rivets, 1/8" rivets and #8 screws. A dimple die for #8 screws is also necessary - mine is cap screw activated and I wore out several of the screws while building the plane - it is needed a lot and I never countersunk when I could dimple. I agree with the earlier posts that suggest that you will develop bad habits and regret trying to get by without the right tools.

Bob Axsom
 
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