×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Drilling holes in thin sheet

Drilling holes in thin sheet

Drilling holes in thin sheet

(OP)
We are having trouble drilling in 11GA 304 stainless steel.
We drill lots of closely packed holes 3/8" od. No matter how we fixture and clamp the sheet to the table the sheet is still warping and creating a gap between the sheet and the table causing vibration in the sheet while drilling. This causes chipped drill bits and eventually broke ones.

We're using a guhring drill specifically for the application and confirmed speeds/feeds w/ guhring.

Any ideas or help?

RE: Drilling holes in thin sheet

Is every thing ridged, both the drill press and work hold device?

What condition is the 304 sheet, like is it half hard, full or somewhere in between?

What you using for coolant?

You didn't post the precision needed so I have to ask, Could you use a perforated plate?

RE: Drilling holes in thin sheet

You can pack the holes a lot closer by cutting them with a laser.
They're expensive, but some outfits do nothing else but contract cutting.
There will be a thin HAZ, so the sheet will 'weld funny'.  If that's important, you can cut the holes a little undersize and take off a few thou with a die grinder.

You can pack the holes just about as close with a waterjet, and with no HAZ, though the sheet will arrive covered with fine abrasive dust that you'll want to clean off.
Again, contract cutting is available.

Either way is probably much cheaper than drilling.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Drilling holes in thin sheet

mielke

Try a "Lip & Spur" drill bit (AKA Brad Point).  These work beautiful on sheet metal and on plastic.

The point is scalloped between the center and margin so that you have a center "point" to accurately start the hole and the lip at the margin cuts only the perifery at first making a clean round hole.

RE: Drilling holes in thin sheet

If you have a lot of these to make, several companies can punch hole through 11 gage plate.   What's the shape of your part, and how many holes are you punching/drilling?   If you need enough parts, the whole plate can be done in one step with a pre-fabbed (but very expensive to make) plate press.

I've used a hand-held electric punch to go through Hastalloy-X plate 5/16 thick.  That worked much faster than drilling.

If you only have a few parts to make - or don't want the expense of an elaborate setup, clamp plywood sheets on both sides of the plate, then drill through the backing plate and steel.

RE: Drilling holes in thin sheet

(OP)
thanks everyone. We're considering laser or waterjet. punching is out of the question (holes are too close together)

Our work surface is as rigid as possible, we have a solid sacrificial plate underneath and we are using flood and thru coolant drills. We're clamping down but i guesse when the drill leaves the sheet its pulling and flexing it. We could clamp down very close to each hole and not have as much as a flexing problem but the vast number of holes we are doing, and them being closely packed, makes this impractical.

I am thinking this problem is happening because of the drill maybe pulling the sheet metal when it exits it and also a small bur on the back sides of the holes is happening which helps create gap between sheet and sacrifical plate. I am hoping another tool may be better, maybe a end mill specifically for drilling?

RE: Drilling holes in thin sheet

(OP)
no we can't use perforated sheet.

RE: Drilling holes in thin sheet

How close is the hole spacing?
Have you tried a spring-loaded clamping device that presses down on the sheet around the drill?
 

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

RE: Drilling holes in thin sheet

(OP)
Like I said I can clamp down very close to the drill hole and get good enough results. But for the shear quantity of holes we are doing it is not pratical to move the clamps to each hole we drill.

We are doing 1000s of holes per sheet of 3/8"OD on a 29/64" triangular pitch.

RE: Drilling holes in thin sheet

Use a spring loaded drill bushing around your drill bit to hold the sheet down. I'll bet someone makes a fixture like that already.  

RE: Drilling holes in thin sheet

How many holes do you need inside a 3" circle?

Given your dimensions I can get 30, but the web thickness for all practical purposes is too thin for drilling.

I would not even attempt this without making an indexable jig from thicker materials using drill bushings.

RE: Drilling holes in thin sheet

We usually sandwitch thin sheets between two sacrificial mild steel plates, clamp down & drill. Decent enough results for our purpose.

RE: Drilling holes in thin sheet

Variation on the 'clamping between 2 sacrificial sheets' idea.

Why not have a 'pattern' piece above with slightly oversize holes, this could act to clamp the part being drilled over almost the entire surface.  Obviously this pattern part will be even more tricky to machine, especially as it will probably need to be a good bit thicker gauge to have adequate stiffness - but you only need to make it once.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Drilling holes in thin sheet

Variation on the 'clamping between 2 sacrificial sheets' idea.

Why not have a 'pattern' piece above with slightly oversize holes, this could act to clamp the part being drilled over almost the entire surface.  Obviously this pattern part will be even more tricky to machine, especially as it will probably need to be a good bit thicker gauge to have adequate stiffness - but you only need to make it once.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Drilling holes in thin sheet

Possibly you can develope a heavy spring loaded 'stripper' on the spindle.  It would press hard on the sheet/stack first before the drill started and stay pressed until the drill retracted.  Similar to a punch and die.  You could even use a guide bushing and guide the drill for even more accurate drilling.

 

99 Dodge CTD dually.

RE: Drilling holes in thin sheet

When you say triangular pitch, I assume you mean 60 degree staggered centers.

It sounds like you are stuck with what you've got unless something can compromise. What is this for?

I would vote for the perforated sheet: if you can go with a slightly larger spacing or a slightly smaller hole diameter or a thinner sheet then a perforator might be able to help.  

Next choice is laser, last is waterjet.

 

RE: Drilling holes in thin sheet

I didn't see mention of a Step Drill bit.  Unless the Guhring bit you mentioned is a step drill.  

I've done custom engine gaskets from very thin copper plate (much thinner and much angrier to drill through than this) and successfully used the sandwich method listed above.  Put 2 pins between the sandwich pieces so that you can use it as a pattern.  

RE: Drilling holes in thin sheet

You really shoud try a lip and spur drill.  Your material might be a lttle thick for it but surely worth a try.  These drills work great on thin sheet metal.

RE: Drilling holes in thin sheet

The dimensions given put the web between holes at .0781", which makes drilling without distortion marginal.

You will kick yourself when you finally try getting a sheet laser-cut.  You could probably push the web between holes down to .01", if open area is important to you.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Drilling holes in thin sheet

as a laser operator who cuts 304 and 316 stainless all day we use nitrogen as assist gas. no HAZ to speak of. only problem i see would be slight warpage of your plate which could be flattened using a roller after operation is complete. each 3/8 hole would take 2.0 seconds including pierce and travel to next hole. laser is the way to go.;

RE: Drilling holes in thin sheet

As someone who's learned this lesson the hard way (we had some soft baffle material in a HX with 3/8" tubes where we ended up drilling the baffles individually - thankfully only 328 tubes):

If you insist on drilling these yourself, you're going to have to reduce the number of plates you put in each stack.

The top portion of the stack shouldn't be too bad, but chip removal might not be the best towards the middle/bottom.  And as you correctly guessed, the sheet would deform slightly (more as you get further away from the clamps) as the drill exits each hole, and the burr behind the sheet when the flex occurs can create additional problems (even if imperceptible at visual inspection, you will hear about it during assembly).

Reduce the number of plates in each stack, and change clamps as much as is practical to keep it close to the work. Or from the sounds of it, change to a different method of manufacture.

Whose bright idea was it to design a heat exchanger that big in diameter with 3/8" tubes?

-TJ Orlowski

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources