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Odd size holes in sheet metal How?

I recently took a job that requires holes in sheet aluminum that are not sizes that standard hole saws or chassis punches can make. There is a series of .86" holes and one that is .84". There are numerous other holes that are easily made with drill bits or step drills and since tolerances are somewhat loose for location, I used a hand held drill motor. I have a hole saw that will make a .90" hole but the customer is thinking that will be to big. I see that Greenlee sells a 13/16" chassis punch but those will be undersized. I did buy a circle cutter but found that it would not go small enough to do what they need and have not been able to locate one that will go that small. I could use a boring tool in the mill but what a pain to figure out a way to clamp the part in the mill. I don't want to make a /circle/hole cutter just for this job. I think that the .90" would be okay for them as they are just holes for electrical connectors but designer engineer customers want what they want and think that they will be to big. Any ideas on how I could make these easily and cheaply?

This is a Sheet Metal Fabricating job. Not a machining job.
It can be done on a Sheet-metal Fabricator, with Unipunch tooling to punch the holes in a punch press or with a Laser Fabricator or Water-jet. Contract the job to someone in that business with the equipment to do it. I see Quality suffering and you losing money doing it in your shop.

Roger
 
I recently took a job that requires holes in sheet aluminum that are not sizes that standard hole saws or chassis punches can make. There is a series of .86" holes and one that is .84". There are numerous other holes that are easily made with drill bits or step drills and since tolerances are somewhat loose for location, I used a hand held drill motor. I have a hole saw that will make a .90" hole but the customer is thinking that will be to big. I see that Greenlee sells a 13/16" chassis punch but those will be undersized. I did buy a circle cutter but found that it would not go small enough to do what they need and have not been able to locate one that will go that small. I could use a boring tool in the mill but what a pain to figure out a way to clamp the part in the mill. I don't want to make a /circle/hole cutter just for this job. I think that the .90" would be okay for them as they are just holes for electrical connectors but designer engineer customers want what they want and think that they will be to big. Any ideas on how I could make these easily and cheaply?

This is a Sheet Metal Fabricating job. Not a machining job.
It can be done on a Sheet-metal Fabricator, with Unipunch tooling to punch the holes in a punch press or with a Laser Fabricator or Water-jet. Contract the job to someone in that business with the equipment to do it. I see Quality suffering and you losing money doing it in your shop.

Roger

Yup, taking a customers requirement of .84 dia. hole up to .90 is sloppy.
You may loose them as a customer altogether, instead of simply declining this work.
 
I had decided to go the modified spade drill route and while looking for them, I came across a circle cutter or fly cutter as suggested by Limi Sami. It was smaller than the one I had recently bought for the job and it looked like that with a bit of grinding, I could make it work. And it did! It made nice clean holes with very little burr. I nearly rapped my knuckles with it while cutting in the drill press as the cross piece that holds the cutter was pretty much all the way to one side and while spinning was about invisible. I started to reach in to pick off a piece of tape or brush away some swarf and felt the wind it created with hairs on the backs of my fingers. Very close!
I wouldn't do anything that was not on the print without discussing it with the customer first. And I agree, it would be sloppy. A guy from their shop came by this morning and brought the part that was to go in the hole. The .9 would have worked okay but with the part and my modified hole cutter, I made it more better. Many times the folks who design or make the drawings have never got their hands dirty and spec stuff from charts and tables not realizing that some variation will still work as required. Yes, a shop specializing in this kind of work could do it properly and I guess they had already gone to them only to get no quotes or lead times outside their schedules.
Thanks for that offer Bugrobo! Very generous of you and thanks to all for your suggestions and comments!
 
I do know that the customer gets lots of no quotes or long delivery times and it is hard for them to get stuff done.
With that sort of specs, it's no wonder. Looks like that is one of those cases where a "Price option" is called for with a "noticeable" difference between a common size hole and the specified odd one.
...lewie...
 
Reminds me of one customer years ago who's engineer delighted in drawing square and rectangular holes in Alu. bulkheads for .......wire runs. Where a round hole would be much simpler and accomplish the same goal. Besides.....where do you get square and rectangular rubber grommets??

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Originally Posted by Gazz

I do know that the customer gets lots of no quotes or long delivery times and it is hard for them to get stuff done.
 
While a properly sized hole is not to be underestimated, I'm always suspicious of specs that call for oddball sizes. He's the customer, so give him what he wants. But kick the dog when you go home, knowing the spec is probably someone's dumb idea.

Engineer: "What do you mean you can't drill a hole around corners? I drew it that way didn't I?"
 
While a properly sized hole is not to be underestimated, I'm always suspicious of specs that call for oddball sizes. He's the customer, so give him what he wants. But kick the dog when you go home, knowing the spec is probably someone's dumb idea.
This could be a case of a part being designed to be made one way and sent out to a shop to be made in a completely different way.
If someone complained about the hole sizes in my drawings I'd be wondering why the f@#$ they're drilling any holes in the sheet metal part at all.
 
Hmmmmm...I don't see where anyone has mentioned that 22mm is a standard size for industrial switches and the like.

Pretty close to your 0.86 and 0.84 inches.....
 
3 flute drill can sometimes be better than two flutes but difficult to sharpen
Sometimes a left spiral, right-cut can avoid suck-up.
gbent mentioned brad points.
Number drill sizes cove many sizes.

drilling through a template/bushing plate/hold-down sheet.

 








 
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