Instructables

Concentric Drilling with a Radial Arm Saw

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Picture of Concentric Drilling with a Radial Arm Saw
This is a piece of round stock into which I have drilled a hole that is perfectly on center.  I could have made the hole as deep as my drill bit is long, but left it shallow.  I did this on my radial arm saw.  What I am demonstrating in this Instructable was inspired by a chapter in the Foxfire Books on boring the barrel for a Kentucky flintlock rifle. 
 
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Step 1: Features of a radial arm saw

Picture of Features of a radial arm saw
My radial arm saw has a 1/2 x 20 threaded shaft on the backside of the motor.  Not only can I attach a saw blade on the front side of the motor, but I can attach a drill chuck or a sanding drum on the backside end.  Further, I can swivel the motor so the shaft runs parallel to the saw arm.  Because the motor moves along the arm on a suspension track, I can pull the motor into something I want to drill.  That would move the motor and bit nearer to the left side of the photo. 

I cut a piece of wood 2 x 3 inches a little over 5 inches long and aligned it under the drill bit so it is parallel to the drill bit.

Rob K4 years ago
I don't  think the the one we have has that potion for the drill chuck. Its a 20 year old Craftsman one.

As for the speeds is it the same or is there some kid of gearing?
Phil B (author)  Rob K4 years ago
My Sears Craftsman 10 inch radial arm saw was purchased new in 1972.  About that time they also made a 9 inch lighter duty model.  A friend has one and I did not see a 1/2 x 20 thd. spindle on the backside of the motor on his saw, only the mechanism for a manually operated blade brake. 

As I mentioned, the Montgomery Ward and Sawsmith saws have a second parallel shaft with a mechanism for adjusting the rpm's of that shaft. 
Scanner2 Phil B2 years ago
Phil and All,
I have a recently acquired 9" Sears radial arm saw. It has the brake mechanism on the motor shaft opposite the blade. I used a block of wood to lock the blade/motor shaft, and removed the brake with the same wrench used for the saw blade. Under that, there is indeed a threaded shaft. I have yet to ascertain the thread size, but I'm betting it's 1/2 inch.
Phil B (author)  Scanner22 years ago
The thread size is 1/2 inch x 20thd./inch so it will fit a Jacob's Chuck and similar accessories. Congratulations on your acquisition. I hope you enjoy it very much.
Rune Cutter4 years ago
Nice, great way to get extra work out of your radial arm.  I've got a drill press that I love for this but it can be tricky, I'm working adding a laser sight to it, just of set to the chuck, or bottom mounted which would allow me to true things up a bit easier, it seems that that would be easy for your rig, you could put the dot right on the end of the bit.
sofjeco4 years ago
Im very hapy at your work
thank'you
Phil B (author)  sofjeco4 years ago
I want to thank you.  I hope you find something useful in the things I have posted.  Best wishes.
From rifle to wood handle...  It's amazing where inspiration can come from.  Good job!
 
Phil B (author)  AngryRedhead4 years ago
Thank you for looking and for commenting.  According to your profile you may be a little young to remember when the Foxfire Books were making their appearance and creating some stir.  If you find them in a library, they are interesting to read.  They are an attempt to document Appallachian culture and methods before those become extinct.   The  chapter on Kentucky rifles had some really simple and clever ways to do very precise operations.
I would highly recommend the Foxfire books as required reading for all makers.  You can find them at many libraries and they are for sale on ebay.
 SIGH.. only if I had downloaded all the books that where available for "free" at www.librum.us/index.html , while they where free .  Any it's worth a visit to the site as the books are now available on CD or DVD at reasonable prices, many demos available as well that are fairly usable, but large files. A lot of old tech stuff is available if you have an interest in that.
It would have been nice to get them for free. I wonder if Google has scanned them...

At least they are widely available.
Phil B (author)  whiteoakart4 years ago
Thanks for your comment.  I just found "Foxfire 5" online.  It is the volume that includes the chapter on gunsmithing.
Have fun. The books are great reading.
Jobar007 Phil B4 years ago
I would be cautious on some of the information in the Foxfire books. One is a remedy for the flu and it involves drinking gasoline.......
You have to take the books for what they are: a documentation of how things were done in Appalachia.   There is one volume that has folk tales that they grew up with, clearly not to be taken literally.  Another has interviews of folks who were in their 90s back in the 1960s.  They just tell stories of what growing up in the mountains was like.

The beauty of the books is that a lot of crafts and skills would have been lost with the passing of these people.  Even though there is no real need to make a chair from woven oak caning, it is a great challenge to do it and teaches you a lot about materials and methods.

I believe the medicinal cure you write of was drinking kerosene, not gasoline. Although, it is not much better.  Kerosene has also been the fuel of choice for fire-breathers.
Phil B (author)  Jobar0074 years ago
The same caution would most certainly apply to things found on the Internet.  The user always needs to apply some tests for veracity, but most of us know that already. 
static Phil B4 years ago
 Foxfire 5 is the only one of the series I own, and found the topic of the making of guns interesting. Particularly the means of cutting the rifling  More likely than not the simple methods produced usable guns. The degree of precision I'm unsure of, as the projectile forced down the barrel was really malleable. To be fair even today, the making a gun barrel striag
Phil B (author)  static4 years ago
I knew a man who made his own long barrel rifle.  He used a percussion cap lock rather than a flint lock.  He bought a surplus military barrel blank.  I think it was for an M1 rifle.  He bored it out and cut flats on the outside to make an octagon barrel.  He made his own rifling tool similar to the one in Foxfire 5.  But, he also had a metal lathe.  I do not remember what he used for a twist guide during cutting the rifling grooves.  The long barrel guides the projectile for a longer duration than a short barrel so that the bullet is on a more precise trajectory after leaving the barrel.  This man shot a squirrel with his rifle.  I think the rifle was .50 caliber.  I remember he told me he made everything for that rifle, himself, except for one spring and perhaps one very special screw.
Jobar007 Phil B4 years ago
I'm not saying that you should ignore the information that is in them, just saying that you should think about what you read and see if it meets common sense (the whole gasoline one.. I can't remember which Foxfire it is in, but I'll see if I can find it).
skunkbait4 years ago
Phil, you never cease to put out great ibles!!!!  My grandfather passed away a few months ago, and I recently got several of his older high-end power tools.  My boys and I are short on cash, so we're always looking for ways to use the tools we already own, rather than buying new stuff.  This really helps!
Phil B (author)  skunkbait4 years ago
Thanks, Barry.  It is good to have contact with you again.  I am sorry to hear about the death of your grandfather. 

This is hardly my favorite Instructable of those I have done, but people seem to have taken to it.  Maybe the title is a teaser suggesting something that just seems impossible.  I pray my Instructables will be a blessing to someone and am thankful to be able to do them.
rob20244 years ago
thanks this clamp is a good idea  -  for best results when boring start with a smaller diameter drill and finish with the final diameter - this causes less vibration and gives a smoother internal suface

rob2024
Phil B (author)  rob20244 years ago
Thank you.  Your observation is a good one.
stoobers4 years ago
This is an interesting way of doing this.  Drilling a concentric hole is one of the hardest things to do in wood.  The grain causes so many problems.

I usually drill a 1/8th inch hole down the entire piece of wood.  It is usually not concentric.  Then I chuck the wood on the wood lathe and turn the outside down to a cylinder.

Voila!

This my two cents:  You might get a straighter hole if you bolted the drill to the table, then mounted the dowel to the saw.  And use a boring bit with one cutting edge instead of a drill bit.  That way, the hole would be concentric, but possibly conical, instead of a non-concentric cylinder.
Phil B (author)  stoobers4 years ago
I had a wood lathe decades before i had a radial arm saw.  I remember an attachment was available for concentric drilling.  It was a tailstock mount for a drill chuck.  The headstock spun the work and the bit bored a hole into the work. 

When I needed to drill a 1/2" hole into the end of the banner pole, a) I did not have concentric drilling attachment for the lathe, and b) the banner pole was longer than my lathe bed.

I have seen the bit wander because of the grain.  I did not have that problem when i bored the banner pole as shown in this Instructable.

Thanks for your comment.
stoobers Phil B4 years ago
Regarding a "concentric drilling attachment for the lathe":

Take the tail stock off and mount the wood on an apparatus similar to your cylinder holder.  Then chuck the boring bar or drill bit in the lathe head and advance the new "tail stock".  That way, the cut is always concentric, but it may be conical :( 

You have some fantastic ideas.

Phil B (author)  stoobers4 years ago
Thank you also for your ideas.
Nice instructable Phil...  I haven't used my saw for boring yet (mostly because of the state of my garage) but this is a good first project...

You could add a clamp such as this one from Rockler to make sliding the jig easier and help with alignment:

http://www.rockler.com/product.cfm?page=16448
Phil B (author)  HowlinPreacherMan4 years ago
Thank you for the link.  I am a tightwad and have used the machine cut edge of a strip of plywood as a straightedge with "C" clamps for hold downs.

I expect you saw other special tasks I have done with a radial arm saw.  If not, just search by means of "radial arm saw."
chrwei4 years ago
you could put a couple holes in the table with lag bolts to attach the jig, this would make realignment a snap.  You could even have multiple jigs using the same mounting holes.

or a drill press vise like this one http://www2.northerntool.com/hand-tools/vises-clamps/item-153813.htm would allow for rather easy adjustment for any one-off holes you want to make.

or if you only want to bore center holes in round stuff, you could get a self centering chuck like these http://www.workholding.com/FINDSELFCENTERINGCHUCK.HTM

Phil B (author)  chrwei4 years ago
Holes through the jig into the table would get a person closer to re-aligning the jig, but there is often a little wiggle in such holes.  In addition, I purposely lowered the arm (and the motor) a little so I did not have to make the uprights taller than necessary.  Using the jig again would mean getting the motor height just right.  A person could get close, but it would not be quite the same the second time.  Thank you for the links.
I love reading about all the amazing things you can do with this tool. My high school  wood shop had one, and I know how great they are to work with. 5 stars.
Phil B (author)  masterochicken4 years ago
Thank you.  I think it is a real shame that radial arm saws are not better known and more respected as precise and versatile woodworking machines.  A lot of owners used them for little more than cut-off saws.  That made it easy for electric miter boxes (chop saws) to displace them.  I have done several Instructables on special applications for radial arm saws.  Often readers ask questions in comments which would not even be asked if people were more familiar with radial arm saws.  But, anyone who wants to buy a radial arm saw can find very good ones for less than $100 on Craig's List.  To me that would be like selling a low-mileage five year old sedan in good running condition for only $500.
Jayefuu4 years ago
Cool :D You could attach a router bit to that for quick mortice and tenons
Phil B (author)  Jayefuu4 years ago
Yes, the drill chuck will hold a router bit, and you could make mortises.  But, my experience is that the bit chatters quite a lot and does not cut cleanly.  One problem is the speed is too low at 3,000 rpm for a router bit to function well.  Radial arm saws by Montgomery Ward Powr-Kraft and by Sawsmith have a second parallel shaft driven off of the main shaft by a variable speed pulley system.  These will produce enough rpm's to power a router bit well.  And, a three-jaw drill chuck is part of the problem.  A collet chuck would be better.  The chatter causes the drill chuck to loosen on its mount so that the chuck wobbles a little.  Using a router bit is not too bad if you stop often to make certain the chuck is tight on the 1/2 x 20 thd. shaft. 
kelseymh4 years ago
It looks to me like you've used the radial-arm saw to make a horizontal drill press.  Is that an accurate summary? 

I'm curious as to how level a typical RAS is likely to be mounted in a home user's shop.  Besides the concentricity issues you discussed, if the throw of the saw is not exactly parallel to the table top, you won't get a good hold.

No, wait, that's not correct.  You used the drill itself to make the holes in your jig.  Therefore, those holes are (by definition) on-axis with the RAS's throw.  If that's not parallel to the table top, that just means the holes in the two uprights will appear misaligned.
Phil B (author)  kelseymh4 years ago
All of the concerns you raised are part of the setup and alignment process on a radial arm saw.  A lot depends on doing the alignment process in the specified order and with the proper care to insure accuracy.  The saw will eventually go out of alignment through use and vibration to some degree and needs to be re-aligned periodically.  Generally, once one of these saws is aligned, you do not relocate it unless you want to take some time to check all of the alignment points.  Thanks for the comment. 
kelseymh Phil B4 years ago
Thanks, Phil!  I know my questions were naive, and I appreciate you taking the time to explain them.
Phil B (author)  kelseymh4 years ago
I am glad to be of help.  Someone quoted Benjamin Franklin as saying all of us are unknowing about something, regardless of what we do know.  That is a big paraphrase, but you get the idea.
Phil B (author)  Phil B4 years ago
Yes, I used a radial arm saw as a horizontal boring machine, or drill press, if you prefer.
rimar20004 years ago
Good work, Phil!! You are very clever!!
Phil B (author)  rimar20004 years ago
Thank you, Osvaldo.