Accepting ones limitations - Page 3 - diyAudio
Go Back   Home > Forums > Design & Build > Construction Tips

Construction Tips Construction techniques and tips

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 30th October 2011, 08:29 PM   #21
Lavcat is offline Lavcat  United States
diyAudio Member
 
Lavcat's Avatar
 
Join Date: Dec 2009
Location: New Jersey USA
This is a timely post for me. I have ancient experience using a drill press, but the projects I have drilled at home have all been with a hand drill, even one panel with over a hundred holes. But it's been years since I've made anything at home that requires drilling, and for my current project I realized my skills with a hand drill would not be sufficient to get my holes to line up, and for this I have little room for error. I have a drill press on order, as I've mentioned in another thread, and I've been reading all the metalworking advice I can find online or get from the library -- books such as Metalworking Tools and Techniques by Stan Bray, Crowood Press, 2003.

My question is about the need for center punching when using a drill press (rather than a hand drill) for making holes in aluminum. My thinking is that with the work and the drill shaft fixed in position, the center punched hole will exert an undesirable lateral force on the bit, however small, because the center punched hole will never be perfectly aligned with the bit. Better, I believe, to use a spotting bit directly without center punching. So far this is theoretical. What do people think?

Then there is the question what type of spotting bit to use! Should the diameter of the spotting bit be the diameter of the finished hole or smaller? What angle to use? Should the angle of the spotting bit be greater than, less than, or equal to the angle of the drill bit? I'd say greater than or equal to, not less than.

Then for aluminum what should be the best angle for the drill bit itself? Some say the softer the metal the more acute should be the angle. What material and coating (if any) is best for the spotting bit and primary bit? Should cutting fluid be used, and if so, what kind?

If a spotting bit of the proper size and type has been used, is there any reason to drill a succession of hole sizes rather than one hole of the final size?

I still have a long wait until my drill press arrives.
  Reply With Quote
Old 30th October 2011, 10:55 PM   #22
diyAudio Member
 
kevinahcc20's Avatar
 
Join Date: Apr 2009
Location: Farmington Hills, MI USA
If by a spotting bit you mean a center drill designed to make a shallow pilot hole to lead the actual drill truely that is a good technique, but as you observe you will not be able to line up that drill to perfectly hit the target if it is just marked. The purpose of using a center punch is to force the drill point to hit the precise target. Like you noted, the drill will actually be pulled sideways into the divot left by the punch. If you have lined up closely just continue drilling. If there is considerable bend in the bit you should reposition to align the drill once the hole is started. Either way if a precise outcome is desired then you should scribe crossmarks for each hole and center punch by walking the punch tip to the intersection of the crossmarks.
__________________
Kevin(ahcc20)...I'd rather have a bottle in front of me than a frontal lobotomy!
  Reply With Quote
Old 31st October 2011, 12:36 AM   #23
Lavcat is offline Lavcat  United States
diyAudio Member
 
Lavcat's Avatar
 
Join Date: Dec 2009
Location: New Jersey USA
Quote:
Originally Posted by kevinahcc20 View Post
If by a spotting bit you mean a center drill designed to make a shallow pilot hole to lead the actual drill truely that is a good technique, but as you observe you will not be able to line up that drill to perfectly hit the target if it is just marked. The purpose of using a center punch is to force the drill point to hit the precise target. Like you noted, the drill will actually be pulled sideways into the divot left by the punch. If you have lined up closely just continue drilling. If there is considerable bend in the bit you should reposition to align the drill once the hole is started. Either way if a precise outcome is desired then you should scribe crossmarks for each hole and center punch by walking the punch tip to the intersection of the crossmarks.
By spotting bit I mean something like this:

Item # 09960635, 120 Futura Coated Cobalt NC Spotting Drills on Hassay Savage Company

Once I get the work properly fixed in position and an origin established, I should be able to move to each hole's coordinates in turn and drill. I should not have to scribe anything. Fixing the work accurately on the table will be a project in and of itself, of course.

Again, I agree with Conrad Hoffman's procedure if I were tying to use a hand drill for this.

For some of what I'm doing I will need 3/8 inch holes, as a pilot for an 15/16 inch chassis punch. For a hole that large (3/8 inch) I am wondering if it would be better to use a 3/8 inch step drill or a regular 3/8 inch twist drill?
  Reply With Quote
Old 31st October 2011, 12:55 AM   #24
diyAudio Member
 
Join Date: Mar 2007
Location: Canandaigua, NY USA
The only time you dispense with the center punch is if using a milling machine and can set X and Y exactly. For all other purposes you center punch. For all purposes, including the milling machine, you use the combined center drill and countersink. On the drill press you still center punch and use the combined center drill and countersink. These do not bend or deflect.

The work has to slide on the table so it will locate itself to the center drill. Use something like Boeshield or Bostik waxes on the table to prevent rust and keep 'em slippery. If the part is small you have to have it in a vise or clamp it for safety, but you'd still start the center drill to locate the part before clamping it. Drills must never drill at an angle due to misalignment between the punch mark and the chuck.

I'm no connoisseur of drill angles and use standard metal working bits for everything except large holes in wood. Then it would be a spade or a Forstner. Or a hole saw. If you're not following the right procedure, no magic angled split point fancy pants drill bits will save you.

Combined center drills and countersinks come in numbered sized from tiny to huge. The most useful is probably the #2, and KEO is a good brand. I do a lot of very small stuff and probably use a #1 more, but that's too small for most home projects. It would be rare that I ever grabbed a #3. Somewhere I have one half the size of my fist, but I've no idea when a person would ever need that. I don't own a drill chuck big enough to hold it!

BTW, those spotting drills are good if you have a milling machine, but really aren't suited for what we're talking about here. They're simply a very rigid drill bit with short flutes, but won't necessarily follow a center punch mark accurately. The tip of a center drill is designed to center on a punch mark, and can do so within less than a thousandth of an inch if conditions are right. The short tip pilots the hole, then the countersink section give the subsequent drill a better guide, if you want to go that deep. Something like this. Failure to use these usually leads to tears.

For aluminum, a squirt of WD-40 is as good as anything. Don't drill dry if you want a clean on-size hole. For wood sometimes a bit of paraffin or candle wax is good on the cutting edges and work surfaces, especially with hand planes.
__________________
May the root sum of the squares of the Forces be with you.

Last edited by Conrad Hoffman; 31st October 2011 at 01:10 AM.
  Reply With Quote
Old 31st October 2011, 02:17 AM   #25
diyAudio Member
 
Neil Groves's Avatar
 
Join Date: Sep 2011
Location: Near San Francisco
i thought you only need lubrication on milling machines or lathes, but thinking about it a drill press is just a milling machine of sorts so that makes sense, i'm still trying to persuade the wife to let me move my workshop to the spare room else i have nowhere to set up a drill press and bench vice, i guess any complicated metalwork i will mark out and entrust to a local engineering firm, once she finds out how much that costs i think she'll let me have my way 8-)

Neil.
  Reply With Quote
Old 31st October 2011, 02:52 AM   #26
diyAudio Member
 
vacuphile's Avatar
 
Join Date: Apr 2011
Location: Not where whatever I am looking for is at.
Conrads advice is right on the money, so it is in addition to the usefull points he makes.

Use a very sharp center punch. A scratching pen is the best I could find for the job. Don't punch too hard, where too hard depends on the material. Alu is really soft, so don't hit too hard. Brass is a lot harder, so it deserves a bit more punishment. The point is that you don't want to create a crater with a caldera, just a little notch to centre the pilot drill. The reason is that the ridges of the caldera might be gripped by your drill, sending it off course. For best precision, don't use pencil or whatever, but scratch with the sharp point of a Stanley knife a cross where the hole has to come (using a steel ruler or straight edge). This allows you to sense where the punch has land. Plus, a cut in a piece of metal is much thinner than anything you can accomplish with a writing material. With some practice you could replace the Stanley knife with point of a caliper, which you slide along the side of your material at the appropriate distance. It is caliper-abuse, but everybody does it, because once you get the hang of it, it is a quick and precise way (if the dimensions of your material are correct).

For wood, don't use metal drills, but the spiral ones with a little guiding point escpecially for wood. Predrill a guiding hole somewhat smaller than this guiding point, and presto.

vac
__________________
Everything is somewhere. Where the @!#$ is it.
  Reply With Quote
Old 31st October 2011, 03:02 AM   #27
Lavcat is offline Lavcat  United States
diyAudio Member
 
Lavcat's Avatar
 
Join Date: Dec 2009
Location: New Jersey USA
Quote:
Originally Posted by Conrad Hoffman View Post
The only time you dispense with the center punch is if using a milling machine and can set X and Y exactly. For all other purposes you center punch. For all purposes, including the milling machine, you use the combined center drill and countersink. On the drill press you still center punch and use the combined center drill and countersink. These do not bend or deflect.

The work has to slide on the table so it will locate itself to the center drill. Use something like Boeshield or Bostik waxes on the table to prevent rust and keep 'em slippery. If the part is small you have to have it in a vise or clamp it for safety, but you'd still start the center drill to locate the part before clamping it. Drills must never drill at an angle due to misalignment between the punch mark and the chuck.

I'm no connoisseur of drill angles and use standard metal working bits for everything except large holes in wood. Then it would be a spade or a Forstner. Or a hole saw. If you're not following the right procedure, no magic angled split point fancy pants drill bits will save you.

Combined center drills and countersinks come in numbered sized from tiny to huge. The most useful is probably the #2, and KEO is a good brand. I do a lot of very small stuff and probably use a #1 more, but that's too small for most home projects. It would be rare that I ever grabbed a #3. Somewhere I have one half the size of my fist, but I've no idea when a person would ever need that. I don't own a drill chuck big enough to hold it!

BTW, those spotting drills are good if you have a milling machine, but really aren't suited for what we're talking about here. They're simply a very rigid drill bit with short flutes, but won't necessarily follow a center punch mark accurately. The tip of a center drill is designed to center on a punch mark, and can do so within less than a thousandth of an inch if conditions are right. The short tip pilots the hole, then the countersink section give the subsequent drill a better guide, if you want to go that deep. Something like this. Failure to use these usually leads to tears.

For aluminum, a squirt of WD-40 is as good as anything. Don't drill dry if you want a clean on-size hole. For wood sometimes a bit of paraffin or candle wax is good on the cutting edges and work surfaces, especially with hand planes.
I plan to use a machinist's vice bolted to this table:

PROXXON - KT 150

I don't want the work to slide at all on the table, as that messes up the coordinates.

I've used a center drill on a lathe many many years ago in school. I don't think I've ever used a center drill on a drill press. Some authorities say to use a center drill when starting a hole on a drill press. Other authorities say this is common but wrong practice and that a spotting drill is the proper tool to use. Still other sources say that if you are using a carbide bit you should neither use a center drill nor use a spotting drill. I am still trying to figure out what is best practice.


Edit: What would be wrong with using a spotting drill to drill the entire hole in one step?

Last edited by Lavcat; 31st October 2011 at 03:09 AM.
  Reply With Quote
Old 31st October 2011, 03:26 AM   #28
Billyo is offline Billyo  Australia
diyAudio Member
 
Join Date: Apr 2011
Location: Sydney
But if using a hand drill, how can you be certain that you are drilling at precisely right angles to the surface?

Will a deep centre punch assist?

I found when drilling a pilot hole through a to-be-detachable panel into the cabinet, because the pilot hole wasnt at a precise 90 degrees, when drilling out the cabinet hole, it wasnt directly under the panel hole... At least... I can only assume it was because I drilled at other than 90 degrees - since the panel was clamped perfectly square to the cabinet when drilling the pilot.
__________________
Epoxy Resin fixes everything!
  Reply With Quote
Old 31st October 2011, 03:35 AM   #29
diyAudio Member
 
Join Date: Mar 2007
Location: Canandaigua, NY USA
Lavcat, you're essentially converting your drill press to a milling machine. Admittedly a bad one, but often good enough for the purpose at hand. Thus, no center punch, just X-Y coordinates. Use whichever type of spotting or center drill suits your fancy, but never ever skip that step if you want your holes located accurately. I'm not sure if spotting drills have clearance or taper, so they might be OK for thin material. Obviously they'll drill a hole! They tend to be expensive and nobody has a full set of different sizes. They are not the tool to use on the drill press when dealing with center punched marks, no matter what "authorities" say! There's a reason the catalogs list them as "NC spotting drills".

Trivia- vacuphile is absolutely right. Old time machinists used nothing more than a steel machinists ruler and a sharp pointed scribe mounted to a post and base for the surface plate. They set the height of the scribe against the ruler, then scribed the (blue/inked) part. With skill and practice it was possible to locate everything to a few thou. A serious user of punches will want what's known as a "bright grind" on the point. That means the grind marks are parallel to the axis of the punch, not around in a circle the way most are done. Yes, I abuse my vernier calipers now and then, but they make hermaphrodite calipers for a reason you know!

I've never managed to drill a hole at 90 degrees to anything using a hand drill. Best I can do is hold a square next to it while drilling, but the results are never perfect. Most people seem to do better at this.
__________________
May the root sum of the squares of the Forces be with you.

Last edited by Conrad Hoffman; 31st October 2011 at 03:40 AM.
  Reply With Quote
Old 31st October 2011, 04:33 AM   #30
diyAudio Member
 
Join Date: Dec 2006
Location: Where the sky loves the sea
If you want it perfect, download the app from frontpanelexpress.com, design it, then send your panel to them to do the milling/drilling. The added bonus is you can get non-round holes and text engraving. The three pieces I have done with them have all come out beautifully.
__________________
"We monitor many frequencies. We listen always. Came a voice, out of the babel of tongues, speaking to us. It played us a mighty dub… "
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Can you help understand limitations of ClassA/G ? Bigun Solid State 86 20th August 2009 04:23 PM
Branch limitations when using includes Circlotron Everything Else 2 2nd May 2008 07:49 PM
LM317 CCS - Any limitations? Archwn Power Supplies 8 16th December 2007 04:12 PM
Capacitor limitations?? kimschips Power Supplies 12 25th March 2005 10:29 PM


New To Site? Need Help?

All times are GMT. The time now is 09:20 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2