Correct Center Drill Depth 2

[Toolingtek]

Currently specifying the C-Drill diameter/number & programming its depth based on the drill bit that will follow it. I try to use a C-Drill large enough to get a funneling action on the following drill bit... Say a #6 C-Drill for a ½” drill bit.
Shop floor operators constantly want to run a standard #1 or #2 C-Drill that is already in the tool changer regardless of what diameter drill bit will follow it. I’ve seen operators edit/replace a #6 C-Drill with a #1 C-Drill and the following drill bit is a ½”.
We have had some issues with hole location. Does anyone know of a written or acceptable procedure?

 

[mrainey]

I think all CNC programmers have seen this problem. It sounds like you're trying to apply a common-sense approach to machining the best possible hole. The operators are doing the same, but with the goal of making holes with the least effort, or maybe they're under pressure to reduce setup times, so they don't take the time to build and/or load the correct center drill.

How about a stubby 90 or 120 degree spot drill, where one size more or less fits all? Good for forming a pre-tap chamfer too. You could do a little testing to evaluate drilled hole location accuracy.

Without shop discipline, on the part of operators and supervisors, no written standard is going to help much.

Just for fun, take a look at my free drill depth calculator. Includes center drills, spot drills, and countersinks. Great minds think alike.

http://bellsouthpwp.net/r/s/rsnmar/Drills.zip

 

[Toolingtek]

I like your ideas but could never standardize a stubby 90 / 120 degree spot drill, half the operators would agree, the other half would not. The first group would try to undermine the second group & so on...
I can't build Rome in a day but a good standard or rule of thumb I could reference on this issue would go a long way.

BTW, I have had some junior programmers download & start using your speed & feed macros; it has been very well received.

 

[mrainey]

There are a lot of articles on drilling at

http://www.mmsonline.com

 

[triggerguard1]

I would second the vote for the 90 deg. spot drill. That's all I've been using for the last 8 years. I tossed all my center drills. PIA big time.

I like running a .5 90deg. spot drill. Takes care of 99% of what I have to drill tap or interpolate later. 90 is the best because of the ease of determining your diameter. You're gonna drill a .375 hole, drop the spot down to .190. Gives you a light chamfer on the hole as well as providing an accurate drill position. Some brands of spot drills will vary on accuracy, but ma ford is top notch. Still, if you're on a budget, key will work fine. Just be sure to creep in on the z depth before you get carried away.

 

[gesigner]

mrainey, Toolingtek;

Where can I download the speeds and feeds macros? I don't see them on the website.
Thanks

 

[mrainey]

proepup,

I'm not allowed to publish a link unless someone asks for help.

It's actually a small, powerful Windows program (beta) that does feed/speed/cycle time/horsepower calculations for different tools and materials. Also has detailed thread data, volume + weight calculator, drill depth calculator, other goodies.

A much-improved update will be available in a week or so. Let me know if you want to be notified.

All free, no gimmicks.

Mike rainey47@bellsouth.net

http://bellsouthpwp.net/r/s/rsnmar/MEConsultantBeta1.zip

 

[BillPSU]

Tapped holes use a 90 degree spot drill producing a chamfer dia larger then thread size and then drill. Drilled hole use screw machine length drill to improve location or spotdrill and drill. Depending on size holes produced, standardize the spot drill diameter, I used 1" dia. Spotdrills are a more accurate tool than a centerdrill and feed length will be shorter. The OD of the drill will be guided by the spotdrill instead to point of the drill which may have inaccuracy in it. Spotdrilling improves hole locations tremendously especially if you use jobber length or longer drills. The disadvantage of a spotdrill or a centerdrill is the additional tool and added cycle time.