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madman
08-02-2011, 12:50 PM
I have been doing some counterboring (actually a LOT of IT Lately) I took on a Contract Position at a temporary agency as a Tool Room Machinist. I HAVE done a LOT of tool steel drilling and counterboring in the Past BUT i have NEVER had the amount of troubles ive encountered with this Material i am now working on. It is A-2 and i counterbore 1/2 inch diameter for 9.5 inches deep. I make extendsions up and am presently running 125 rpm, at .005 thou per rev feed. Anything else just wouldnt even work. As it is it is jumpy all the way through the blocks. I have tried putting a LOT of pressure on it to get it to bite in and stoop its jumping but nothing seems to work? HM?? Just curious what youd suggest ourt tooling isnt the best there but ive not had this problem before >? Any Hints Guys ? Thanx Mike

TGTool
08-02-2011, 01:00 PM
I presume the counterbore is because they need the flat bottom hole down there at the 9-1/2" depth. But that doesn't mean that the whole depth needs to be produced by the counterbore. I'd be inclined to drill down 9-1/4" with a regular twist drill that can be resharpened much more easily and just hit the bottoms of the holes with the counterbore.

I'd also be suspicious of the cutting edges of the counterbore after that much work in A2 and that would be consistent with what you're experiencing. If they can't or won't get the tool resharpened if it needs it, can you do a little judicious dressing with a Dremel tool?

Dr Stan
08-02-2011, 01:17 PM
2X on TG's recommendation as its exactly what I would have said.

Toolguy
08-02-2011, 01:23 PM
I would get a long spade drill that uses replaceable carbide tips. The carbide comes in pointed and flat end. Drill most of the way with the pointed end, then change to the flat end to finish up. You will still need to keep the RPM reasonable and use coolant or oil to not burn up bits, but it would go a lot easier. I prefer the AMEC brand of spade drills.

Black_Moons
08-02-2011, 01:34 PM
My first thought would be dull tool.

tdmidget
08-02-2011, 03:11 PM
A 9 1/2 " counterbore? Why? The purpose of a counterbore is normally to put the head of a fastener flush or below. It sounds like you need fasteners 9 inches longer and a new engineer. 9 inches is approaching gun drill territory. A counterbore is not intended for such use. The solution may be as above to drill part way and finish with the counterbore. If the drill wanders then your pilot on the counterbore may not line up or be in a bind, resulting in a broken counterbore stuck in an obviously expensive workpiece.

TGTool
08-02-2011, 03:25 PM
Drill wandering is certainly a possibility on a deep hole, but I'd think the concentricity wouldn't be much of an issue here. If he drills the smaller diameter first, it will tend to keep the 1/2" drill following the small diameter wherever it may lead. And if he drills the larger diameter first, he's got the cone of the drill to help center the smaller diameter tool. A little more iffy in this case since the web will leave something more like a shallow concavity rather than a center drill or spotting drill start but probably sufficient.

Carld
08-02-2011, 05:52 PM
I agree with tgmidget, why in the world would a real engineer do that in A2 steel. That borders on ignorant and tells me he don't know what he is doing. Just use a long bolt.

That's about the dumbest thing I have ever heard. A2 is hard enough to work with without making it even harder to do.

madman
08-02-2011, 10:37 PM
Well i DO agree with you guys BUT in the world of contract Machining do like the print. I do like the idea of the larger drill to suit the bore xcept for the last 1/4 inch or so. I been drilling counterboring a toin of stuff and this shops the first time i have had these things occurr. Thanx Mike

madman
08-02-2011, 10:38 PM
This is why im there to do all the stupid things they arent willing to i guess? Sometimes i just want to give up. Later Thanx Mike

DATo
08-03-2011, 06:22 AM
I presume the counterbore is because they need the flat bottom hole down there at the 9-1/2" depth. But that doesn't mean that the whole depth needs to be produced by the counterbore. I'd be inclined to drill down 9-1/4" with a regular twist drill that can be resharpened much more easily and just hit the bottoms of the holes with the counterbore. -TGTool

*** TWO THUMBS AND A BIG TOE UP ***


I agree with tgmidget, why in the world would a real engineer do that in A2 steel. That borders on ignorant and tells me he don't know what he is doing. Just use a long bolt. - Carld

Carld, I routinely work with PhDs and trust me there is no correlation between a title appended to a name and basic common sense. The best way I've ever heard it put is ... They have a lot of intelligence and no brains.

beanbag
08-03-2011, 06:35 AM
"Drilling 9 inches is one thing, but COUNTERBORING 9", wow that's going to cost you a whole lot more." ;)

form_change
08-03-2011, 07:49 AM
I agree with the idea of drilling 9 1/4 inches and then counter boring the last 1/4". I have a couple of drill bits sharpened with flat bottoms that I use for precisely that purpose. Drill with a standard drill and clean up/ flatten the hole with the square bit. Not difficult to sharpen off-hand either.

While I rarely bother to defend engineers, for those slagging off at them I'll mention a lesson that was taught to me many years ago by one of my better bosses. I walked into his office one day complaining about a stupid design and he sat me down and proceeded to ask me a series of questions about the design and what it was intended to do. After a short time of me revealing my total ignorance, he pointed out that only the designer knows exactly what a design is intended to achieve and why it was done that way. While the rest of us might think we could do better, as soon as we do we take on all liability and responsibility for the item, which as we don't know why things were done that way in the first place, may even be more likely to fail. I've met some abysmal engineers but I've also met some great ones who's good ideas have been derailed by tradesmen who knew better...

As an example, I once worked in a machine shop with 6 or so machinists. There was one medium sized lathe there that no one wanted to use as the compound slide screw was tight in one spot when it revolved. It had been like that for ages. It took me all of 15 minutes examine it, take it apart and find the high spot where the screw had been bent and straighten it. After that, every one said that it was fine. I hadn't trained as a fitter, but I did wonder why one of the machinists (some with 20+ years of experience) there were not able to diagnose and fix this relatively simple problem.

Back to the issue at hand, I can think of at least two reasons why a deep counter bore might be better than a long bolt, and (with apologies for any offense caused to Mike) if someone came to me saying that they had to cut 9 1/2" with a counter bore, I'd be wondering why they didn't drill most of it in the first place before I called the designer ignorant.

Michael
(Mindful that there but for the grace of God go I...)

Carld
08-03-2011, 12:34 PM
form_change, I agree with what you say. Had I been given that job I would have asked to talk to the designer/engineer and asked why it needed to be counterbored 9 1/2" deep. I would have then suggested alternative ways that would be better and faster. Had he/she refused those suggestions I would have told him the cost to do it as designed would be high and on his dime.

Since madman is working for them and not doing it in his shop when the shop finds out how long it takes and how many counterbore cutters it takes they WILL convince the engineer to change his plans if cost is an issue.

If the cost to do the job is no problem let the work begin and the customer pays for time, material and cutters.

Many was the time I was given a job and when I looked it over I would tell the shop owner this is not the best way and will take a lot of time. He would look it over and decide whether to work it out with the customer or just do it and charge him as needed. Most the time when a customer found out the cost was to be high they decided on changes as needed.

gwilson
08-03-2011, 12:45 PM
Yep,counterbores were not designed to do deep hole drilling. Can you get a regular type long drill ground with a pilot on it's tip? That will keep the drill from wandering. But,drilling the holes with successively larger drills till you get to the one you need will also help keep the hole centered. Of course,they'd all have to be long drills.

bborr01
08-03-2011, 01:14 PM
I would do as suggested in several previous posts and drill with a c'bore size drill then c'bore the last little bit.

No worries about the drill wandering as it will follow the through hole. Period.

Edit to add: Not long drill, TAPER LENGTH drill.

Brian

Magnum164
08-03-2011, 01:43 PM
This is what bothers me on internet forums. As a drawing checker I look at drawings to verify that they can be manufactured and a lot of times do make recommendations for changes. However, you have to know the design the application in order to do that.

For this part, there are several reasons why someone may want to bolt closer to the mating surface. Load distribution comes to mind as well as there could be something that needs to go in that hole above the bolt, perhaps a spring - operating much like a shock.

When I send work out and am questioned about the design, the work goes somewhere else... that tells me the shop does not have the capability to do the work.

baldysm
08-03-2011, 06:07 PM
I'll jump on the bandwagon and support the drill til the last bit and then counterbore it.

It's true, that as a temp/contract guy, it's best that you do as your told, and not worry so much that it makes sense.

That being said, a bolt 9" long (or whatever) doesn't have as much holding force as a bolt a few inches long, especially if the stress/pressure is perpendicular to the axis of the bolt.

I used to be a diemaker, and we always had fairly short bolts, even in tall parts, and had to drill/counterbore them quite deep.

form_change
08-03-2011, 06:35 PM
Just realised that I missed out a sentence in my previous post - between the second and third paragraphs I should have said something like "Engineers aren't the only ones who do (or don't do) odd things. Tradesmen are known to do them too.

Certainly as a contractor you are basically there to do what you are told. It may not make much sense but as you are only temporary the chance is that you have been told even less about the job in hand than the permanents.

The other possibility I thought of for this job was that the steel was going to be shaped after assembly into something (a form or die block for example) and so fasteners were counter bored deeply so that subsequent operations wouldn't hit them.

When I think about the work to drill a 9" hole and the extra work to put a flat in the bottom, I'm not even sure I'd bother questioning it - finding the right person to ask would probably take longer than changing drill bits.

Michael

gzig5
08-03-2011, 06:45 PM
Why is everyone bashing the engineer/draftsman that specified a nine inch deep hole with a flat bottom? :confused: I don't see where it was mandated to use a counter-bore to make the hole. There very well could be a good reason for the dimensions of the part. It is up to the manufacturer to determine the best way to make the part to the dimensions and finish specified and then quote the cost based on that method.

Black_Moons
08-03-2011, 07:15 PM
Many was the time I was given a job and when I looked it over I would tell the shop owner this is not the best way and will take a lot of time. He would look it over and decide whether to work it out with the customer or just do it and charge him as needed. Most the time when a customer found out the cost was to be high they decided on changes as needed.

Theres also the matter of: Time spent talking to the customer costs you money, Unless you are charging him for it, And then how much does convincing him to change the design cost him verus save him?

DR
08-03-2011, 08:07 PM
Deep counterbores are not uncommon at all in die making.

For the OP's application I'd probably drill and finish flat hole bottom with a reground drill.

Speaking of counter boring tools.....over the years I purchased a number of different brands, American made and a few "quality imports", none third world though.

Weldon Tu-lip were the only ones worth anything, but have a price to match their quality.

John Stevenson
08-03-2011, 08:36 PM
When I send work out and am questioned about the design, the work goes somewhere else... that tells me the shop does not have the capability to do the work.

Two side to that coin.
I have been given jobs where I had had to ream a 28.39 hole in sheet steel, queried the size as it's a non entity and told "Just do it"

So new reamer reground to size and jobs away. Later it turns out this hole was for a rubber grommet.
On that same job holes reamed at 14mm and 18mm to H7 tolerance were for M12 and M16 bolts to secure this backplate for a cable distribution box. :eek:

Magnum164
08-03-2011, 09:13 PM
Two side to that coin.
I have been given jobs where I had had to ream a 28.39 hole in sheet steel, queried the size as it's a non entity and told "Just do it"

So new reamer reground to size and jobs away. Later it turns out this hole was for a rubber grommet.
On that same job holes reamed at 14mm and 18mm to H7 tolerance were for M12 and M16 bolts to secure this backplate for a cable distribution box. :eek:

I can agree... Questioning dimensions is understandable, but the design is what I was talking about.

Carld
08-03-2011, 11:28 PM
There is nothing wrong in asking the customer a question about a job. In fact, to me it's shows concern about the work. A simple question like does the bolt hole really have to be counter-bored that deep seems fine to me. If they say it does then I would ask if it can be drilled oversize and counter-bored at the bottom. If not I would drill it undersized and then counter-bore it.

To assume they are not equipped to do the job because they asked a question and then pull the job is foolish.

bborr01
08-04-2011, 12:11 AM
I just re-read the OP.

The OP said he had been doing a LOT of counterboring lately. Twice.

If it were a single hole, I would probably do like has been suggested many times already. Drill the clearance hole, then the counterbore diameter drill, then flat bottom it with a counterbore or a drill that had been sacrificed to make a flat bottom hole.

If it was a LOT of holes, it would probably be worth questioning it and keep making chips until you get an answer.

It also depends a lot on if the designer is right up the aisle or if it is a matter of "have your people get in touch with my people".

Good question though.

Brian

Magnum164
08-04-2011, 12:32 AM
To assume they are not equipped to do the job because they asked a question and then pull the job is foolish.

Re-read my post. That is not what I said. There is a difference in asking questions and questioning the design...

mochinist
08-04-2011, 12:38 AM
I think reading text on a forum like this doesn't always read as intended by the author. Carld, John and Magnum all make good points. An engineer/designer/guy_that_figured_out_how_to_use_a_cad_program, I work with a lot, I will call and ask when I see something that is maybe a little out of the ordinary and I'll ask what they are trying to accomplish/do/etc, and explain why that may cost more...or hey, I do what I'm good at, and am not afraid of a challenge, but this part may better for a different type of shop. I cant do everything, thank you for the chance to quote.

I cant tell you how many times I have gotten a call asking why a quote was high and then after a few minutes talking it comes out that they never bother to edit the tolerance block that is calling out for plus or minus .001" on all three place dimensions(english), and the holes can be drilled instead of bored and a saw cut finish would be fine for the edges:rolleyes:







as for the 9" deep cbore, I would drill it out like the others suggested and then finish it with a flat bottom drill or make an extension for a cbore

beanbag
08-04-2011, 03:44 AM
If you didn't actually counterbore the hole, could they really tell? ;)

Carld
08-04-2011, 10:30 AM
"beanbag asked, If you didn't actually counter-bore the hole, could they really tell?"

Probably not and since the counter-bore works best when it has the pilot in a guide hole the hole may end up looking drilled anyway. I think drilling it under size one drill size and then using a drill bit ground flat on the end to finish it out would be the best of all methods.

I've made drills like that as well as grinding a pilot on the end like a counter-bore cutter. You really don't need to use a counter-bore cutter for a deep hole like that and you don't have to ask the customers permission as long as the hole is to the print.

If it's a customer that gives you a lot of work you may or may not ask him about drilling or counter-boreing because you know each other well enough.

If it's a bid for a job you need to ask him because of costs involved.

Carld
08-04-2011, 10:50 AM
Magnum164, actually, if you question why the counter-bore needs to be that deep you would be questioning the reason it's designed that way. Even if you just asked can I counterbore deep enough for the bolt head you would be questioning the engineers intent.

Depending on the attitude of the engineer he/she may or may not take offense. Most the engineers I asked about something on a print would listen and then just say yes or no and may explain. A few would get a little surly and tell me to do what the print shows and I did.

Magnum164
08-04-2011, 01:29 PM
Magnum164, actually, if you question why the counter-bore needs to be that deep you would be questioning the reason it's designed that way. Even if you just asked can I counterbore deep enough for the bolt head you would be questioning the engineers intent.


True.. That was my point:) Guess I should clarify. My position is a little different. Generally someone in manufacturing is involved in the design review. So you would not be questioning one person's design, you would be questioning a design that has gone through at 15-20 people including a manufacturing person. By the time the drawing is sent for actual production, they know what they want - just a part.

If something is to be left up to the shop, it is generally flagged as "PER STANDARD SHOP PRACTICE"... Then it can be made with an ice pick as long as it meet's the dimensions on the drawing.

Carld
08-04-2011, 04:26 PM
We're more or less on the same page.