Back Yard Mechanic needs to Drill 7/8" Hole

[Gordon Gould]

Hi All,

I am building a road grader. It is a low (as possible) budget project.
I am not a machinist but have a lot of patience.
I have almost finished cutting all the steel pieces and will need to drill four
7/8" and two 3/4" holes in 3/8" material for the lift arms and top link pins.
It looks like two drill bits from McMaster_Carr will run me about $100 . Or I could just get the 7/8" bit and use a bushing on the 3/4" top link pin.
QUESTION:
My drill press has a 1/2 hp 1750 rmp motor. I get a 5:2 speed reduction
using my slow speed pully for 700 rpm. Can I drill a 7/8" hole with this??
Or is there a better (cheaper) way ?

Thanks.

 

[Matt_Jr]

I don't see why not. I drilled a 3/4 inch hole in my back blade pivot plate(around 1/2 inch thick or more) with a hole saw in a hand drill. Real slow, and lots of oil. Good luck.

 

[firefighter jim]

hole saw.

 

[J_J]

Carbide tip hole saw and some cutting oil.

 

[Oasis]

Cheaper, yes. $36.99 plus shipping

I have been using a set of these for a couple of years. They are holding up just fine but I don't drill big holes very often.

Link:

- Harbor Freight Tools - Quality Tools at the Lowest Prices

Harborside cut and paste:

8 Piece Silver and Deming Drill Bit Set

Top quality M2 high speed steel bits
Can be used in any electric drill or drill press with a 1/2'' or larger drill chuck
Black industrial finish
Precision ground

Includes handsome fitted wooden storage case. Shank: 1/2"; Sizes: 9/16", 5/8", 11/16", 3/4", 13/16", 7/8", 15/16", 1"
Shipping weight: 4.3 lbs.

ITEM 527-8VGA

$36.99

 

[GE222]

I tend to differ. Hole saws are great for rough holes, but are not the most accurate.

You should be able to find those bits for less than $100. If you are only purchasing them for this project only, try harbor freight, or one of the big box stores. Import bits are fine for occasional use. Drill a pilot hole first, around 3/16". Then go with the big bits. Don't try to use an intermediate bit such as 3/8" or 1/2". Again, as mentioned, use lots of oil.

If a slightly oversized hole is all you need, then use a hole saw. Again use lots of oil.

Try to use enough pressure for a descent spiral of chips, without stalling the motor. Use caution when the large bits are about to break through, as they might grab.

 

[westcliffe01]

Looks to me like you can get a 5/8" & 7/8" spotting drills AND a 1" capacity chuck for the $100 at Enco. The spotting drills are shorter, more rigid thus more practical for the application. Your local hardware store (Sears) should have drill bits in this size with reduced diameter triangular shanks to prevent them slipping in a smaller chuck.

From a safety point of view you need to do 2 things:

1, Clamp the plate to the table of the drill press with at least 2, better 3 G clamps. The danger is not highest when actually drilling, but when pressure is let up or the drill backed off to release shavings.

2) Look at the drill cutting edge. Notice how the drill helix angle creates a very sharp cutting edge that tends to "bite" hard into the material being cut. While drilling a hole, this edge can be your friend, speeding up the process. However, when the outer edge of the drill breaks through the back surface, there can be a tendency to lift the plate off the table of the drill as the unfinished edge of the hole rides up the drill helix. This hazard can be reduced by removing the helix angle from the outer 1/16"th of an inch of this cutting edge. I tried to sketch this in the attachment below.

Enco - Guaranteed Lowest Prices on Machinery, Measuring Tools, Cutting Tools and Shop Supplies

Enco - Guaranteed Lowest Prices on Machinery, Tools and Shop Supplies

Enco - Guaranteed Lowest Prices on Machinery, Tools and Shop Supplies

 

[tessiers]

I use hole saws and winshield wash fluid, it works great, is cheap, and a lot less mess. I would be quite surprised if you could notice the difference in the hole size with your application, maybe will find the hole saw will give you a hole slightly oversized, better to slide a pin into. Another option would to bring the parts to a machine shop, they would probablly drill or punch them cheaper than even the hole saws would cost.

 

[SkunkWerX]

For lift arm and top link pins hole saws will work fine. I have Cat 1 attachments that are pushing 20 years old with pin holes cut by hole saws. Bi-metal (white) hole saws can be had at Lowe's and Homedepot, with mandrels for about $12 or so.

I agree with Oasis about the Silver and Deming bits from Harbor Freak.
For $39 it's hard to go wrong. If you envision building several projects, this would probably be a good buy. I have this same set , and have used the 3/4" and 1" bits extensively.

If anyone is wondering what a hole saw will do, I cut [2] 1 1/4" holes in 1" thick steel recently with a Lenox Bi-metal holesaw. Go slow, keep it cool with fluid, and most importantly with holesaws, the work must stay perfectly still, clamped tight.
I like the Lenox bi-metal blades for my Sawzall, as well.

 

[radman1]

You should be able to find some cheap bits. Cheap bits do ok if you start with small hole and work your way up to larger. Start with 1/4, then 1/2 or 5/8, then 3/4 or 7/8". Use lots of oil. ATF works ok and is cheap. I have a cheap set and they will do the job.
Unlike an earlier post, I tend to use the intermediate sized bits but don't make your steps in size too close because a small change in size makes the larger bits bite to much on the edges. A drill press is much easier to control than a hand drill with large bit. My drill press can run about 500 rpm. Still a little bit fast for the larger bits but you should be ok at 700 rpm.

My set is similar to the HF set.

 

[jmc]

Cheaper, yes. $36.99 plus shipping

I have been using a set of these for a couple of years. They are holding up just fine but I don't drill big holes very often.

8 Piece Silver and Deming Drill Bit Set
Top quality M2 high speed steel bits
Black industrial finish
Precision ground
Includes handsome fitted wooden storage case. Shank: 1/2"; Sizes: 9/16", 5/8", 11/16", 3/4", 13/16", 7/8", 15/16", 1"
$36.99

Like Oasis, I've had good luck with my set of S & D twist drills. Sounds like the same set except my wooden case is anything but handsome! Anyway, 700RPM is about 50% too fast for drilling 7/8" in mild steel. Once they overheat, they'll lose there hardness so don't push them too hard for too long.

 

[Egon]

Try a machine shop.

 

[Gordon Gould]

Thanks for all the feed back. I never thought of a hole saw.
I was mostly concerned about the 700 rpm on my drill press.
It seems a little fast to me for a 1/2" hole so I was worried
about a 7/8" but I sounds like I should be OK.
If the hole isn't perfect nobody will notice - I cut all the steel
plate with a Sawzall. I clamped a couple of angles back to back
on either side of the cut line to use as a blade guide. Actually it came out
pretty good. Think I'll look for some cheap drill sets.
Thanks alot.

 

[2manyrocks]

What are the advantages of using windshield washer fluid as a lubricant? I've heard of using ATF, but this is the first time I remember anyone suggesting washer fluid.

I've not had good luck with large, cheapo drill bits. Seems like I ruin them pretty quickly.

 

[Window Geek]

Whenever we've had to cut holes in machine tabletops, we've used the Lenox hole saws too. Portable, way less tailings and easy to spot. The windshield wash takes the heat away and keeps the metal from sticking (melting) to the saw teeth. I've used water with a little dish detergent in a tank sprayer with great results too. We've cut through 1 1/4" steel plate with a hand drill in about 10 minutes. It's great for big bolts and hose passages.

 

[captaincrab55]

Carbide tip hole saw and some cutting oil.

I use the cutting wax... I've drilled hundreds of 7/8" with the same carbide tip hole saw with cutting wax in heavy duty commercial grade panels...

Don't take it the wrong way, cutting oil will work too.

 

[westcliffe01]

My drill press has a double reduction belt drive so I am sure I can get down to around 250rpm. I believe I only paid about $100 for it at Menards. It is a floor standing unit.

The slowest part of hole drilling is punching the first hole through. A 1/4" high quality drill is the best (you can afford to buy several in such a small size). Key with drilling is to never let the drill rub. From the get go you need lots of pressure (proportional to the drill size) to keep the cutting edge cutting. A continuous string of swarf should emerge and ideally flood it with coolant to keep the temperature down.

3/8" is not very thick material, unless you overheat the drill and dull the edge. A technician who fitted a tow hitch to my Cobalt spent 15 minutes trying to drill a single hole through a high strength reinforcement on the floorpan (it was just over 1/16th thick). It was alloy steel that was harder than he expected and his drill bit was blunt. He put a jack under the drill to get more force but all he got was the tip of the drill glowing red hot. I walked across the street to a hardware store and bought a new drill and he put it in and it went through like butter.

A job I had years ago required special hard drawn chrome copper bar to be drilled through from end to end with an 11mm hole. There were about 500 of these parts, ranging in length from 2ft to over 6ft. The special copper itself was air freighted from Australia, the only place in the world it was available within the need lead time. I then had all that copper bar cut to length and sent to a small arms manufacturer more than 600 miles away, who had a high power gun drill that could process all the bars in a short time. All the material had to make the trip there and back across africa without being stolen (the value was a significant fraction of the then gold price). Those holes were so perfect that any one of them would have make a good smooth bore rifle. We paid them to run their machine, plus they kept the drilled out core as valuable scrap, I'm sure it was a good deal for them... Some time later I needed a piece of material to make a special 3" diameter washer and had the storeman slice me off a piece a bit more than 1/4" thick (was the finished size) and after he weighed it he said the material alone for the washer was worth more than $5 (that was in 95 !) I'm sure if I had screwed up that job, they would have tied couple of "useless" bars around my ankles and sunk me in the bay...

 

[PILOON]

Recently I needed a fairly close tolerance 3/4" hole.

While hole saws cut well when lubed, they end up in a loose fit. SO, I ground off the outside staggered teeth to be flush with the drum (bell).
Was surprised to find
A -cutting was excellent, in fact better than with staggered teeth.
B -no binding and cleaner cut
C -teeth no duller, perhaps even better.

Staggerd teeth are much better for wood in that wood binds due to sawdust while metal does not swell like wood.

I lubed with what I had on hand; WD40.

I have even bored 3" holes in 1/2" plate with a quality hole saw on my press drill. Worked fine!

 

[BHD]

if one has a cutting torch one can cut a rough hole and then weld in a bushing or a shaft collar,

 

[cowsrus]

I always thought those hole saws were strictly for wood, just by looking at the teeth on them. I never dreamed that you could drill holes in thick steel until i read this. I can't wait to try it out.