Twist Drill Angle with Center Drills vs Spotting Drills

[petertha]

I know drilling thin metal isn't the same as thicker stock, but the small increment 'progressive' type drilling seem to rely on this principle to make good circular holes. Mind you, I've also wondered if what also helps make these work has as much to do with a preferable rake angle vs. regular twist drills even if you tried to mimic with the same series of drill sizes.

 

[EmilioG]

Using the tip of a center drill/Csnk. isn't a bad idea if you're using 118° drill bits. I found 145° spotting drills in a range of sizes from MA Ford.
They make them all the way down to 3mm/1/8". I'll use them with my 135-140° drills.

 

[Downunder Bob]

I believe this is what Bob K. suggested earlier but the guys lightheartedly gave him grief for not mentioning it until after they already ordered/bought their spotters but I agree with you - it works.

The guys are amusing, don't get me wrong I love this site, One can learn so much here and, unlike some others, it is friendly What I find amusing is the way they go on about spotting drills as if it was the end of everything in the world of machining. Like i said before the only spotting drills I had ever heard of were the ones we had to make as a project as apprentices. Some people call them step drills, They are used to spot face a surface around a drilled hole, particularly on a casting, so that a bolt has a flat square surface to tigten against, I still have my set They were also used to countersink holes for SHCS to set below the surface, My set of five drills is designed for 1/4", 5/16", 3/8", 7/16" and 1/2" SHCS.

I can't help but think the guys have never done it tough, and had to make do with the tools at hand. Most of the machines we had when I was an apprentice were known as "Wartime finish". which meant no time, money, or effort was used in making them look nice, sure,they worked fine and were good machines, they just looked unfinished, and that is how they stayed.

There were of course no digital instruments at all. No DRO's No CNC, every thing was done manually A few of the toolmakers had their ownn 6" or150 mm vernier calipers, most of our toolmakers were imigrants from war torn europe, out of 12 toolmakers only two were Australian born and trained, another three were from UK, and the rest came from various parts of Europe. In many ways probably the best apprenticeship a guy could have, as we were exposed to all the different engineering cultures of that time. Everyone had a 1" or 25mm mic, for larger sizes we had to get the 0 - 6" mic from the tool store, this mic had a set of changable fixed anvils that would allow it to be set up to measure all sizes from 0 to 6" I could go on, but I'm sure you get the picture

 

[Bob Korves]

The guys are amusing, don't get me wrong I love this site, One can learn so much here and, unlike some others, it is friendly What I find amusing is the way they go on about spotting drills as if it was the end of everything in the world of machining. Like i said before the only spotting drills I had ever heard of were the ones we had to make as a project as apprentices. Some people call them step drills, They are used to spot face a surface around a drilled hole, particularly on a casting, so that a bolt has a flat square surface to tigten against, I still have my set They were also used to countersink holes for SHCS to set below the surface, My set of five drills is designed for 1/4", 5/16", 3/8", 7/16" and 1/2" SHCS.

I can't help but think the guys have never done it tough, and had to make do with the tools at hand. Most of the machines we had when I was an apprentice were known as "Wartime finish". which meant no time, money, or effort was used in making them look nice, sure,they worked fine and were good machines, they just looked unfinished, and that is how they stayed.

There were of course no digital instruments at all. No DRO's No CNC, every thing was done manually A few of the toolmakers had their ownn 6" or150 mm vernier calipers, most of our toolmakers were imigrants from war torn europe, out of 12 toolmakers only two were Australian born and trained, another three were from UK, and the rest came from various parts of Europe. In many ways probably the best apprenticeship a guy could have, as we were exposed to all the different engineering cultures of that time. Everyone had a 1" or 25mm mic, for larger sizes we had to get the 0 - 6" mic from the tool store, this mic had a set of changable fixed anvils that would allow it to be set up to measure all sizes from 0 to 6" I could go on, but I'm sure you get the picture

Remember, Bob, this is a FORUM where we TALK about machining. This is not our shops. You seem happy to tell your stories as well, and they are good ones. Conversations on forums like this tend to gravitate toward the BEST possible solution to any project or operation. Obviously, none of us have the tools, machines, and skills to do everything that is suggested. The great part of our discussions, in my mind, is really thinking and digesting what we are planning and doing on a certain operation, not just doing it by rote the same way grandpa told us to. That is how we improve our skills in a lonely home shop, with no shop foreman or coworkers to help us out. Not all shops here are equipped the same, the hobby machinists here have widely differening mixes of skills and backgrounds, and we have a universe of different project and work flow ideas. I think we all benefit from hearing the whole spectrum on how to drill a hole, for instance, from quickly punching a hole in a piece of scrap to creating a demanding bolt pattern as best as we can do it with our resources. Additional skills, more ideas, and a wider outlook can do nothing but help our approaches to doing good work in our shops, in my opinion. If readers of the posts think that means they need to buy a brand new machine and tooling for every operation they do, well, that is a personal problem. I try to offer cheaper, quicker, and simpler approaches to doing something in my posts whenever appropriate. This wonderful and useful forum is all about learning and sharing. Like on any forum, we all need to separate what makes sense to us from what does not.

 

[mikey]

The guys are amusing, don't get me wrong I love this site, One can learn so much here and, unlike some others, it is friendly What I find amusing is the way they go on about spotting drills as if it was the end of everything in the world of machining. Like i said before the only spotting drills I had ever heard of were the ones we had to make as a project as apprentices.

I enjoyed your description of your experiences, Bob. Would that more of us had the benefit of the kind of training you got but the fact is that what you learned decades ago, many hobby guys are learning for the first time here, on HM. We are not in the trade; we are here by choice and interest and a lot of us are learning things on the net, possibly for the very first time. What you may see as the guys making a big deal about spotting drills, I see as growth and learning in a hobby guy as something is made clear for the first time. Remember that you are coming from a background in the trade, whereas most of us are skilled workers or professionals in our own fields that just happens to not be machining; this is new to many of us.

I'm just a hobby guy that has been bumbling his way along for about 30 years now. I know that it is not enough for a hobbyist to just know what. He must also know why and how and when in order to develop a skill. When someone provides that for him, a light bulb often goes off in his head and he understands. Some of the guys get excited when this happens; I get it.

I know you get it, too, so when you can, teach us. But don't just tell us what; tell us why, how and when. You may not always see it in the posts that follow but I guarantee you that some hobby guy sitting in his shop will be smiling because you opened a door in his mind.

 

[Downunder Bob]

Remember, Bob, this is a FORUM where we TALK about machining. This is not our shops. You seem happy to tell your stories as well, and they are good ones. Conversations on forums like this tend to gravitate toward the BEST possible solution to any project or operation. Obviously, none of us have the tools, machines, and skills to do everything that is suggested. The great part of our discussions, in my mind, is really thinking and digesting what we are planning and doing on a certain operation, not just doing it by rote the same way grandpa told us to. That is how we improve our skills in a lonely home shop, with no shop foreman or coworkers to help us out. Not all shops here are equipped the same, the hobby machinists here have widely differening mixes of skills and backgrounds, and we have a universe of different project and work flow ideas. I think we all benefit from hearing the whole spectrum on how to drill a hole, for instance, from quickly punching a hole in a piece of scrap to creating a demanding bolt pattern as best as we can do it with our resources. Additional skills, more ideas, and a wider outlook can do nothing but help our approaches to doing good work in our shops, in my opinion. If readers of the posts think that means they need to buy a brand new machine and tooling for every operation they do, well, that is a personal problem. I try to offer cheaper, quicker, and simpler approaches to doing something in my posts whenever appropriate. This wonderful and useful forum is all about learning and sharing. Like on any forum, we all need to separate what makes sense to us from what does not.

You are quite right Bob, And I apologise to anyone and everyone who feels that I unfairly critisized them and or their way of doing things. Yes this is a forum and it is a great one at that.

My training was a long time ago 1961 -1966. I've probably forgotten much of what I learned, and I'm often frustrated by the new fangled way of doing things.

This discussion on drill points intrigues me, because I don't remember ever using a drill with a 135deg point, in fact I don't recall ever seeing one for sale or anywhere else. I have only ever used 118 deg drill bits often with the point split, or partially split. Occasionlly I will sharpen a drill in a different way say for drilling sheet metal or brass. I will also round the shoulders on a drill when I need a very accurate hole that cant conveniently be bored. Drilling the hole to 1/64th or 0.5mm or less if possible undersize then follow through with the on size drill with rounded shoulders will act like a reamer, giving a clean hole that is on size.

When the location is importand I've always started my drilled holes with a center drill. I believe a correctly sharpened drill will drill straight and pretty close to on size once it is started like this.

 

[Downunder Bob]

I enjoyed your description of your experiences, Bob. Would that more of us had the benefit of the kind of training you got but the fact is that what you learned decades ago, many hobby guys are learning for the first time here, on HM. We are not in the trade; we are here by choice and interest and a lot of us are learning things on the net, possibly for the very first time. What you may see as the guys making a big deal about spotting drills, I see as growth and learning in a hobby guy as something is made clear for the first time. Remember that you are coming from a background in the trade, whereas most of us are skilled workers or professionals in our own fields that just happens to not be machining; this is new to many of us.

I'm just a hobby guy that has been bumbling his way along for about 30 years now. I know that it is not enough for a hobbyist to just know what. He must also know why and how and when in order to develop a skill. When someone provides that for him, a light bulb often goes off in his head and he understands. Some of the guys get excited when this happens; I get it.

I know you get it, too, so when you can, teach us. But don't just tell us what; tell us why, how and when. You may not always see it in the posts that follow but I guarantee you that some hobby guy sitting in his shop will be smiling because you opened a door in his mind.

Thanks Mikey, I will try to accept the position of teacher, although I think there are many here who do a better job of that than I could ever do. I don't have the patience, I find as I'm running out of time, and far too many things to do. My other half has been very unwell these last 14 months, so I spent very little time in my shop, although she is now on the mend and recovering well, so hopefully more shop time coming up.

I will continue to add my ten cents to any discussion that I think I can offer something too. I will also try to be alittle less blunt.

 

[mikey]

Thanks Mikey, I will try to accept the position of teacher, although I think there are many here who do a better job of that than I could ever do. I don't have the patience, I find as I'm running out of time, and far too many things to do. My other half has been very unwell these last 14 months, so I spent very little time in my shop, although she is now on the mend and recovering well, so hopefully more shop time coming up.

I will continue to add my ten cents to any discussion that I think I can offer something too. I will also try to be alittle less blunt.

Sorry to hear about your spouse and I hope things continue to go well.

Bob, you weren't blunt or critical. You have a different perspective than us hobby guys and I think we all respect that; I just wanted to share from the other side of things, that's all. We're glad to have you on HM and look forward to whatever you have to share.

 

[woodchucker]

This disagrees with some of the info shared here. Source: http://www.guhring.com/Documents/Catalog/Drills/NCSpotDrills.pdf

If using a HSS or HSCO drill, choose a spot drill with a smaller point angle (i.e. spot with a 90° drill, follow with a 130° drill)

For a carbide drill, choose a spot drill with a larger point angle (i.e. spot with a 142° drill, follow with a 140° carbide drill)

Thought I would post it, as I am always forgetting the rule. I do like spotting drills on some tough to center , tough to line up holes.

 

[Mitch Alsup]

So, this thread advocates going directly to the size of hole you want without drilling smaller sizes out first.
What is the backup plan if your lathe/drill press/mill does not have enough power to drill the hole in one step?