Small Diameter Deep Hole Drilling

Rogue_Machinist · May 31, 2021

So first things first, GUN DRILLING ISNT AN OPTION, I recently ran a batch of parts. 16 of them. Well only 15 were needed but I always like to have a set up piece. I need to drill a .250 diameter hole 6.9" deep. But the problem im coming across is half of the parts the holes will be relatively straight and straight enough. And the other half have about .020" of runout/deflection. These parts are being peck drilled on a lathe using a cobalt drill 135° in 4140. Is there a way to get them all to run true so the new batch I need to run arent bad? I am currently doing a #3 C.D. then a .250 screw machine to 1" deep then pecking the remaining with the long cobalt drill. Will adding a second jobber length drill help at all?

And lastly would this issue be solved by having these parts drill in a CNC mill be a better option for the runout?

Any and all input is greatly appreciated.

Triaged · May 31, 2021

Is is it a coolant through drill? What are you holding the drill with? What coolant pressure do you have?

yardbird · May 31, 2021

You never came back, how did your 1/2"-14 NPT parts turn out? Are you using an aircraft style drill? That's a long 1/4" hole.

I've seen them high pressure coolant through carbide drills do some crazy long holes in one shot.

Brent

litlerob1 · May 31, 2021

Drop the center drill and use a spotting Drill with equal tip angle. Letter D Screw machine Drill, Letter D Jobber, Letter D Longish Drill (6.7" full flutes), .25 Aircraft extension Drill. Be done.

R

Rogue_Machinist · May 31, 2021

litlerob1 said:
Drop the center drill and use a spotting Drill with equal tip angle. Letter D Screw machine Drill, Letter D Jobber, Letter D Longish Drill (6.7" full flutes), .25 Aircraft extension Drill. Be done.

R

Company wont buy a spot drill, hell they dont even know what a spot drill is. LOL. My shop is stuck in the 1970s. But its perks are awesome so I wont leave. Yet. Ok well I can also say they wont buy these drills so I need to find a different option. Its a blind hole and they just dont want to listen to me.

Rogue_Machinist · May 31, 2021

Triaged said:
Is is it a coolant through drill? What are you holding the drill with? What coolant pressure do you have?

No through coolant. And I made a bushing for the drill that is concentric to within .0002". And coolant pressure is just a coolant spray with a g83 full retract peck cycle.

Rogue_Machinist · May 31, 2021

yardbird said:
You never came back, how did your 1/2"-14 NPT parts turn out? Are you using an aircraft style drill? That's a long 1/4" hole.

I've seen them high pressure coolant through carbide drills do some crazy long holes in one shot.

Brent

Oh and to add, those 1/2"-14 NPT parts I was taken off that job as it was "no longer hot" even though it was due in April.

litlerob1 · May 31, 2021

nissan300ztt said:
Company wont buy a spot drill, hell they dont even know what a spot drill is. LOL. My shop is stuck in the 1970s. But its perks are awesome so I wont leave. Yet. Ok well I can also say they wont buy these drills so I need to find a different option. Its a blind hole and they just dont want to listen to me.

Okay, only use the center drill a tiny depth, enough to locate the Drill. -.025 or so.

Tell your boss to read this Thread. And tell him I am the foremost hole making expert in the Western Hemesphere. Buy the Tools to do the job.

Robert

Rogue_Machinist · May 31, 2021

litlerob1 said:
Okay, only use the center drill a tiny depth, enough to locate the Drill. -.025 or so.

Tell your boss to read this Thread. And tell him I am the foremost hole making expert in the Western Hemesphere. Buy the Tools to do the job.

Robert

He wont want to spend the money. Trust me. My main lathe is 31 years old and is on its last leg and he wont replace it. It goes through 1 gallon of way lube a week and leaks hydraulic fluid. Cant run under 400rpm without stuttering. Yeah I dont think hes going to buy the right drills.

litlerob1 · Jun 1, 2021

nissan300ztt said:
He wont want to spend the money. Trust me. My main lathe is 31 years old and is on its last leg and he wont replace it. It goes through 1 gallon of way lube a week and leaks hydraulic fluid. Cant run under 400rpm without stuttering. Yeah I dont think hes going to buy the right drills.

Time to look for another job. I can't work with people like that.

angelw · Jun 1, 2021

nissan300ztt said:
He wont want to spend the money. Trust me. My main lathe is 31 years old and is on its last leg and he wont replace it. It goes through 1 gallon of way lube a week and leaks hydraulic fluid. Cant run under 400rpm without stuttering. Yeah I dont think hes going to buy the right drills.

Well, I reckon he deserves the shitty parts being made.

With regards to your question of whether drilling on a CNC Mill would be better, in terms of hole straightness and lack of run out, in order of worst to best it goes like this:

1. Stationary work-piece, revolving drill
2. Revolving work-piece, stationary drill
3. Drill and work-piece counter rotating

Regards,

Bill

metalmadness · Jun 1, 2021

nissan300ztt said:
He wont want to spend the money. Trust me. My main lathe is 31 years old and is on its last leg and he wont replace it. It goes through 1 gallon of way lube a week and leaks hydraulic fluid. Cant run under 400rpm without stuttering. Yeah I dont think hes going to buy the right drills.

WTF is the deal here, a fucking spot drill costs $30. Your "boss" wants to do some crazy shit drilling a 1/4" hole 7" deep...well guess what it takes specific tools to do the job. So unless you use the right tools then this whole process is going to suck ass.

My $0.02....carbide/hss spot drill with equal drill point angle, carbide jobber drill to 1.5" depth. SOLID CARBIDE aircraft drill OR similar 'gun-style' drill. Mitsubishi Carbide makes excellent drills that I think you can get up to 50xD or somethign like that. I used to drill .2188 holes 6" deep all day in 4140 with theses specific drills and very rarely broke a drill. Now with a hole that deep running carbide, you better believe TSC is gonna be needed. I wouldn't even try it in 4140 without TSC.

If your "boss" wants this job done, they either need to outsource it or get with the damn times and use the right tools.

If the hole actually needs to run true, then a solid carbide drill is THE only option IMO.

Of course you know best though

metalmadness · Jun 1, 2021

litlerob1 said:
Time to look for another job. I can't work with people like that.

LMAO he's fine burning thru $30 worth of waylube per week but doesn't want to buy the right tools.

OP, ur fckd on this one. What are these benefits you speak of that make leaving this job impossible?

Mtndew · Jun 1, 2021

If I were in your shoes, I'd drill and bore a pilot about 1/2" or so, then drill to depth.

If I were in a normal shop, I'd spot drill, pilot drill, and then deep hole drill with TSC.

Curious though, you say the benefits are good, compared to what? Have you looked at what other shops are giving their employees? You might be missing out.

CAMasochism · Jun 1, 2021

litlerob1 said:
Okay, only use the center drill a tiny depth, enough to locate the Drill. -.025 or so.

Tell your boss to read this Thread. And tell him I am the foremost hole making expert in the Western Hemesphere. Buy the Tools to do the job.

Robert

As the secondmost expert in hole making I concur with litlerob. Metalmadness is also correct Mitsubishi MVS drills are excellent at deep drilling. Though you need a mill that can spin them at the proper RPM as well as coolant pressure.

metalmadness said:
LMAO he's fine burning thru $30 worth of waylube per week but doesn't want to buy the right tools.

OP, ur fckd on this one. What are these benefits you speak of that make leaving this job impossible?

The bosses wife?

implmex · Jun 1, 2021

Hi nissan300ztt::
You wrote:
"He wont want to spend the money. Trust me."

I assume this is why you say gundrilling is not an option.
So could these be drilled from both ends?
Could they be drilled undersized from both ends and then reamed from one end to eliminate the step in the middle.
If you cut the business end of the reamer down so the flutes are only 2 diameters long you can follow a fairly snaky hole...it won't be straight but it'll be centered at both ends and maybe straight enough not to matter.

Another way to get the best long holes possible with twist drills is to drill an inch deep undersized, bore to size as deep as you can and then run your final sized twist drill using the first inch as a drill bushing to help keep the drill centered and pointing down the axis of the hole.
Use aircraft drills (if you have any), split the point, keep them super sharp and don't feed the shit out of them.
Halve your normal feedrate so you don't inchworm the drills when you push them into the stock.

Shit job, shit tools, and a shit boss...sometimes all you can do is a shit effort and fake the shit out of it.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Edit: Mtndew beat me to it, but I'd try for a bit deeper than 1/2 inch for the pilot hole.

GENERALDISARRAY · Jun 1, 2021

Since doing it the right/efficient way is a no go. And not knowing at all what the part looks like.

You can drill the hole first, then establish the OD concentric to the drilled wonky hole. Which means re-processing the part and at least an extra op.

Rogue_Machinist · Jun 1, 2021

metalmadness said:
LMAO he's fine burning thru $30 worth of waylube per week but doesn't want to buy the right tools.

OP, ur fckd on this one. What are these benefits you speak of that make leaving this job impossible?

Not impossible to leave. But 4 day work week 1 shift. Come and go as I want (I can come in late an hour or leave half a day whenever I want). Wages are damn fine for this area. And not many actual machine shops around here, most are button pusher jobs paying $15/hr or less. Plus he matches up to 10% of my 401k if I so desire to put that much in. And I can make whatever I want on my own time before work, lunch after lunch. Or come in Fridays and do what I want.

angelw · Jun 1, 2021

nissan300ztt said:
Not impossible to leave. But 4 day work week 1 shift. Come and go as I want (I can come in late an hour or leave half a day whenever I want). Wages are damn fine for this area. And not many actual machine shops around here, most are button pusher jobs paying $15/hr or less. Plus he matches up to 10% of my 401k if I so desire to put that much in. And I can make whatever I want on my own time before work, lunch after lunch. Or come in Fridays and do what I want.

It seems like your boss is making a small fortune in that business; someone gave him a large fortune and he's working on it from there. All those benefits cost money and he can't shell out for a drill. Sounds like BS to me

metalmadness · Jun 1, 2021

nissan300ztt said:
Not impossible to leave. But 4 day work week 1 shift. Come and go as I want (I can come in late an hour or leave half a day whenever I want). Wages are damn fine for this area. And not many actual machine shops around here, most are button pusher jobs paying $15/hr or less. Plus he matches up to 10% of my 401k if I so desire to put that much in. And I can make whatever I want on my own time before work, lunch after lunch. Or come in Fridays and do what I want.

Hmmm I dunno dawg...I make a fantastic wage and have all of the benefits you describe, plus unlimited (yes unlimited) PTO. And yet, my boss gives me free reign to buy damn near whatever tooling I need to get the jobs done.

Your gig sounds legit for sure, that is hard to give up for anyone. Other shops around me pay 'similar' for lead programmers but, 'similar' isn't exactly a good enough reason to leave a good spot, so it would need to be a big increase.I would recommend you talk to the dude since it sounds like you are pretty tight, and talk to him about what it takes to machine competitively. Some things just cost money and, youll lose money on this if you do it the wrong way.

I've worked in shops where they don't want to pay for the needed tooling or whatever it is... I tell them XYZ and they still say, "no we don't want to, do it with what we have"....well the process inevitably fails and I go to them and say "see, I told you" and they end up buying the shit I suggested in the end anyway. Except now they wasted 4 billable hours on nothing.

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