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.