counterbores - a hole within a hole?

[zeeprogrammer]

Soon, if all goes well, I'll be starting another project. I'm doing a little research to see what is involved. Page 1...a counterbore. I haven't got one.

This has raised a number of questions and two goals...

Goal 1 is what/where to purchase such an item (drawing calls for 0.24" or ~15/64"). What I've seen so far is 'relatively' expensive. Please note the word 'purchase'...I'm not ready to make my own tools. On the other hand, I would certainly entertain alternatives. For example, my inexperienced mind would simply take a 15/64 drill bit and drill to the required depth. While I understand the shoulder is not optimal to hold a screw...it should be sufficient for this model. Another alternative might be that the diameter of the counterbore really doesn't matter. So why not take a 0.25 end mill and plunge to the desired depth? (This assumes you drill first then end mill without moving the table. Otherwise accuracy is 'iffy'.)

Goal 2 is to get a better understanding of 'counterboring'. Why, how, where, when, tools available, etc. So my hope is that this post might generate some interesting responses.

I did a little search on this fine forum and came across an interesting post by Bernd. Here it is.

http://www.homemodelenginemachinist.com/index.php?topic=1295.msg9327#msg9327

I put this link here so that others may find it.

Why else does one counterbore? So far I understand that counterboring allows you to put in a screw that can't stick out of the material it's in, yet provides sufficient shoulder to hold it.

I see that there are 'solid pilot' and 'interchangeable pilot'. It seems that an interchangeable pilot allows you to mix the counterbore diameter with different diameters of the hole through which whatever goes in. That is, more flexibility when dealing with the various screws/bolts etc. that have different diameter heads but the same thread diameter.

Not knowing much about this tool/procedure...I'm struggling to even know what questions to ask. This will be remedied as I learn more.

Thanks.

 

[Foozer]

Soon, if all goes well, I'll be starting another project. I'm doing a little research to see what is involved. Page 1...a counterbore. I haven't got one.

This has raised a number of questions and two goals...

Goal 1 is what/where to purchase such an item (drawing calls for 0.24" or ~15/64"). What I've seen so far is 'relatively' expensive. Please note the word 'purchase'...I'm not ready to make my own tools. On the other hand, I would certainly entertain alternatives. For example, my inexperienced mind would simply take a 15/64 drill bit and drill to the required depth. While I understand the shoulder is not optimal to hold a screw...it should be sufficient for this model. Another alternative might be that the diameter of the counterbore really doesn't matter. So why not take a 0.25 end mill and plunge to the desired depth? (This assumes you drill first then end mill without moving the table. Otherwise accuracy is 'iffy'.)

Goal 2 is to get a better understanding of 'counterboring'. Why, how, where, when, tools available, etc. So my hope is that this post might generate some interesting responses.

You got the understanding down, counter bore, spot face, etc to have a surface perpendicular to the hole, let the bolt head or nut rest squarely upon what is an irregular surface or as you described, sitting the fastener out of sight. HERE for a type I have used way too many times.

Interchangeable pilot types do as you say, increase the range of usage.

They must be used with the pilot or it'll be chatter city. They work well but the type shown does have a small radius so a square flat bottom hole it wont make. They be not on the cheap side. But if you want to avoid the "Walk" problem yet to be overcome with using an end mill ( 2 flute end mill walks on me too ) then the piloted counter bore is the ticket.

Robert

 

[steamer]

You can make them also.....here's a fairly complicated hole done with a fairly simple co-bore I made.

Reply 56 has pictures.....

http://www.homemodelenginemachinist.com/index.php?topic=3951.45

Dave

 

[zeeprogrammer]

Robert: Thanks. As for the counter bore shown...you say it must be used with a pilot. So the total price is $23 + cost of pilot. That's better than $6 a hole. Well...I did say I'm in this for the long run...but ouch. That's 1/3 the cost of the kit. In any case, am I correct about the pilot? What would I get?

Dave (steamer): Uh oh...someone didn't read the entire post maybe? I wasn't looking to make. On the other hand...I am interested in 'how to make'. So how did you make it?

Well this response is taking a while. Got distracted by Dave's thread. I'll need to keep an eye on it. By the way...'little girl's hands'...got a daughter eh? I've got two. Talk about salt and pepper, sweet and sour, joy and pain, peak and valley. I'm not talking about the differences between them..it's what they put you through.

Thanks guys. I can call you guys right?

 

[mklotz]

You're right to not attempt to make a tool like a counterbore yet. Besides, in this case, I don't think it's cost effective.

I got along without them for many years, using end mills as you suggested. The exact size of the CB hole almost never matters. Note that end mills do not produce a flat-bottomed hole. Examine one carefully and you'll see that the cutting edges have a very slight taper from center to edge. For CB purposes it's almost never important.

I generally recommend not buying sets and buying the individual tools as you need them but, in this case, I'll make an exception. This set:

http://www.use-enco.com/CGI/INSRIT?PMAKA=368-0050&PMPXNO=947730&PARTPG=INLMK3

covers all the commonly-used number size screws and is only $35. It should cover all your small engine building needs. (0.24" is the size needed for a #6 screw.) Later, if you get into larger models, you can flesh it out with a few larger sizes (e.g., 1/4, 5/16, 3/8, 1/2) bought singly as you need them.

Oh, remember that, in use, counterbores are turned clockwise viewed from above.

 

[zeeprogrammer]

Thanks Marv!

Oh, remember that, in use, counterbores are turned clockwise viewed from above.

Oh har de har har. :big: :big:
That was good.

 

[Foozer]

Robert: Thanks. As for the counter bore shown...you say it must be used with a pilot. So the total price is $23 + cost of pilot. That's better than $6 a hole. Well...I did say I'm in this for the long run...but ouch. That's 1/3 the cost of the kit. In any case, am I correct about the pilot? What would I get?


Thanks guys. I can call you guys right?

What mklotz said, just ordered a set for myself. Not building space shuttles with the FAA looking over every tool used. One I showed is a bit overkill, and is not found of deep holes, just happened to be the type I've used. The exampled kit looks like it will handle a deeper cut. Measure the pilot on the counter bore, drill pilot hole to match + a thou or two, counter bore the hole then full size the pilot hole. Only advantage to changeable pilots is if the hole is already full sized (or odd sized) and you need pilot to match

As long as Guys is spelled with a "U" its fine

 

[steamer]

Yes you should have a basic set of standard couterbores. I do and I agree.

However.....making a cutting tool is not only cost effective for the odd job, but is fun and rewarding too.

It is a great learning experience and something to add to the skills......if your cutting brass, it doesn't even need to be hardened.

Basic D-bits are something that you should learn how to make as they can really get your bacon out of a fire for a few pennys worth of 0-1 rod and a few minutes work.

Theres no real magic here.....

I'll send something to you Zee if you like. I have some articles but would rather not post them on the forum as I don't know the copyright provenence.

Dave

 

[zeeprogrammer]

Thanks Robert. Given my debacle earlier with 'beet' vs 'beer' I can not guarantee proper typing. So please give benefit of the doubt should you see any odd typos in the future. ;D Man it was tempting to have some fun with this.

Dave: You're absolutely right and several people (Marv certainly springs to mind) have suggested same. Learning how to make the tools is different from learning how to use the tools. (But I understand that knowing how to make the tools gives better insight and experience in using the tools.) I'll get there. I've sent you my email address.

 

[Stan]

Marv gives you good advice. I bought those sizes of counterbores from Enco many years ago when they cost about $2.00 each and they have given good service.

The secret to counterbores is the pilot. It has to be a close fit in the drilled hole to keep the counterbore centered. If you buy the machine screw sizes, then the pilot fits the machine screw size clearance hole. Interchangeable pilot counterbores are a pain and making pilots for them an even bigger pain

 

[Mainer]

If 'twere me I'd probably use a 1/4" end mill and call it close enough.

 

[Stan]

Mainer: If you drill a hole on the mill and then change to an endmill it works OK. If you drill a bunch of holes on the drill press, to use an endmill you have to put it on the mill and center it for every hole. Still works good but very time consuming compared to piloted counterbores you can use on the drill press.

 

[steamer]

Oddball diameters and depths call for a differant approuch, and a piloted counterbore turned up for the occasion really works well.

Dave

 

[zeeprogrammer]

So for the newbie like me...the last 3 posts show how there's more than one answer for a given task. A lot depends on the spec of the task, the cost, the time, and whether it's how you make your living, if it's a hobby, and if a hobby...how much of a purist you want to be. All are right of course.

So for the four holes I have to do, and all the time in the world...I'll drill then mill one hole at a time.

 

[steamer]

Which ever way gets the counterbore in is the right way.... :big:

Dave

 

[rake60]

I won't claim it to be right, but every counter-bore I've ever done
was drilled to the print specifications followed by an end mill that
was .030" over the head diameter of the socket screw to be
accommodated.

Rick

 

[Stan]

Rick: Two questions. Do you do your drilling on a mill and do you have end mills ground to size for your counterbores?

 

[rake60]

Yes I do drill all holes on the mini mill. (My X2)
I bought a cheap import set of end mills that range from
1/16" to 1/2" in 1/32" increments. Those are what I use
for counter bores.

Rick