Spot drill question

[mirek1017]

question ,I need to drill over 300 .120 dia holes in SS316     .5 deep .I should spot first ?

I want to use carbide coolant thru drill 

[Aaron Eberhard]

Talk to your drill provider for their recommendations.   In general, with a 135° drill in a good machine, I only spot drill afterwards to deburr/edge break.

If you do spot drill, make sure you're using the proper angle.  Harvey has a good guide here:  https://www.harveyperformance.com/in-the-loupe/choosing-spot-drill/

[rgrin]

If you're going to spot for a chamfer/edge break afterwards, why not just do it prior to drilling? Just so that way you can use a 90° spot and get that perfect aesthetic? Just curious. I had an old programmer pose that question to me awhile ago and has stuck with me and I typically spot prior to drilling. I find that spotting after can be a little harder since the tool wants to chatter unless I slow the RPM way down. But if I spot prior the chamfers almost always look minty

[Aaron Eberhard]

53 minutes ago, rgrin said:

If you're going to spot for a chamfer/edge break afterwards, why not just do it prior to drilling? Just so that way you can use a 90° spot and get that perfect aesthetic? Just curious. I had an old programmer pose that question to me awhile ago and has stuck with me and I typically spot prior to drilling. I find that spotting after can be a little harder since the tool wants to chatter unless I slow the RPM way down. But if I spot prior the chamfers almost always look minty

Because I'm not going to be using a 90° drill bit, and that will wear out/notch the outer edge of the drill, especially a carbide one.  There's no problem spotting before hand, but make sure you use a spot an appropriate angle.  For a 135° drill bit, I like to use a 140° spot.

It's almost always just as faster or faster to use a quality chamfer mill to clean up the edges if you're not getting a good finish out of your spot drills.

Edit:  I will note that I'm specifically talking about harder materials..  If you're doing A36 or aluminum or something, it hardly matters Do whatever works well for ya!

[Jake L]

On 7/7/2023 at 2:08 PM, mirek1017 said:

question ,I need to drill over 300 .120 dia holes in SS316     .5 deep .I should spot first ?

I want to use carbide coolant thru drill 

Another thing to consider is the tolerances. Are you opening up the hole after drilling, or is the drill finishing the hole? What is the tolerance on the location of the hole?

These are usually the driving questions for whether or not we spot for our drills.

[mirek1017]

No tolerance on holes ,after drilling I need to make some 10 deg  lead hole 

 

[CNC CHRIS]

58 minutes ago, mirek1017 said:

No tolerance on holes

EVERYTHING has a tolerance. 

[Tim Johnson]

On 7/7/2023 at 2:08 PM, mirek1017 said:

question ,I need to drill over 300 .120 dia holes in SS316     .5 deep .I should spot first ?

I want to use carbide coolant thru drill 

If you have true 316 SST there should be no problem but true 316 barely exists anymore. If you have what is the now normal 316/316L you might want to start with 25 to 50 holes and take a look at your drill. The included low carbon of 316L is your drill's enemy.

[byte]

21 minutes ago, Tim Johnson said:

If you have true 316 SST there should be no problem but true 316 barely exists anymore. If you have what is the now normal 316/316L you might want to start with 25 to 50 holes and take a look at your drill. The included low carbon of 316L is your drill's enemy.

If the surface is flat sure, but if this is a casting I think you'll get better life spotting first 

Also flatness

On 7/7/2023 at 2:24 PM, Aaron Eberhard said:

Talk to your drill provider for their recommendations.   In general, with a 135° drill in a good machine, I only spot drill afterwards to deburr/edge break.

If you do spot drill, make sure you're using the proper angle.  Harvey has a good guide here:  https://www.harveyperformance.com/in-the-loupe/choosing-spot-drill/

I know for aerospace stuff like honeycomb panels, the tool manufacturer info I've seen was so far from reality, I feel like some providers tells you to run it too hot so you burn through more tools, but maybe I'm paranoid

[cruzila]

21 hours ago, CNC CHRIS said:

EVERYTHING has a tolerance. 

plus or minus zero

[Aaron Eberhard]

17 hours ago, byte said:

I know for aerospace stuff like honeycomb panels, the tool manufacturer info I've seen was so far from reality, I feel like some providers tells you to run it too hot so you burn through more tools, but maybe I'm paranoid

There's no helping you aerospace panel guys...  Your tooling reps should be therapists...

 

 

Seriously, it's always a trade off of time vs. tool life.   Which one is printing more money.  It's very hard to do an honest tool life evaluation unless you're running true production parts, because if you're doing less than X holes enough to actually wear out tools repetitively, there's too many other variables about what affected tool life.   That feeds through from what the tooling reps get as far as information goes to give out.  How many of their customers are running a similar part to yours, on a similar machine, with similar work and tool holding?    Are those customers drilling as many holes as you need to, and do they prioritize tool life vs. production speed the same way you do, etc.?

[byte]

Couldn't have said it better Aaron