Help! Part 2 of Enlarging Holes in Stainless Plate: Off-Center Enlargment

A while back, I asked about enlarging holes in 1/4" thick stainless plate
(Type 316). Here's a summary of the job I've been tasked with:
There are forty-four stainless square support posts. Each post has a base
consisting of two pieces of 1/4" thick stainless angle plate; the plates are
welded along the bottom of the posts, one on each side. Like this:
H
H
_]H[_
The two horizontal flanges that make up the base each have two holes (four
holes per post) for bolting the base to a concrete pad. The holes were
drilled 1/2" by the factory, but need to be 13/16". That's where we left off
in my last request for advice in this newsgroup.
Now I find out the job might be trickier.
Two of the holes may be too close to the forward edge of the plate after
enlargement (still awaiting further info from the customer). If so, then
half the holes (88 of the 176) will not only have to be enlarged, but will
need to be offset so that the resulting enlarged hole is no closer to the
forward edge of the base plate as it is now.
Any ideas on the best way to do this? I have access to a Rong Fu Mill-Drill.
If this were plain carbon steel, I'd probably use an end mill to "drill" the
hole on a new center. But I'm not sure how well that will work with 316
stainless.
Thanks for your advice!
Michael
Reply to
DeepDiver
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Right idea. Wrong machine. I've never used one of these Rong Fus so I don't know for certain, but I don't see how they would be anywhere near rigid enough. Be sure and use a low speed and a high feed when you do this. You don't want to workharden the cut.
You'll want a few spare endmills. Personally, I'd use 2 flute HSS here. But others may disagree.
Karl
Reply to
Karl Townsend
Suggest dont give up your day job just yet.
Reply to
PrecisionMachinisT
"Karl Townsend" wrote in message news:bX77e.5540$ snipped-for-privacy@newsread1.news.pas.earthlink.net...
Well, that's the only mill I have available (unless we farm the job out to a professional shop). In which case, my part in the whole problem is finished.
But actually, there is one advantage mill-drills have over their larger brethren for jobs like this: you can swing the head on the column. Normally, that is considered a disadvantage (and I agree) because you can't make z-axis changes without losing your zero. But for this job, I have to get to the holes from the bottom of the plate because they are too close (horizontally) to the post to get to them from the top. I don't know of many home-shop mills out there that can fit a 48" post under the mill head. But with the mill-drill, I can clamp this part upside down, with base on the edge of the milling table and the post off the side (hanging towards the ground), and then swing the head over to get to the holes.
Why two-flute instead of four-flute?
Thanks, Michael
Reply to
DeepDiver
Plasma cutter
Gunner
Rule #35 "That which does not kill you, has made a huge tactical error"
Reply to
Gunner
If you had a plasma cutter, you would not have asked the question. So I am assuming that you don't. The Drill / Mill should work well once you figure out how to clamp the part. Lowering the head so the column is short will help on the rigidity.
The best way would be to use a hole saw or a 13/16th drill. Drilling is one of the most efficient ways to remove metal. The forces are balanced and both lips are continuously cutting. Use coolant and fairly low speed. Be sure to keep cutting at a feed fast enough that you are under the metal that has been work hardened on the previous revolution. Not feeding enough is a mistake. If you have to sharpen your drill, give it a little extra clearance.
Carpenter Tech has a great booklet on machining Stainless Steel.
Dan
Reply to
dcaster
I'm beginning to think that you need to do just that.
Actually there's a good number of them out there. They're called horizontal mills and this job pretty much screams for one.
I've got a good bit of experience plunging end mills into a interrupted cut in 316 SS and I must say that I have serious doubts about a mill-drills rigidity being good enough. I was doing it on a huge Cincinnati #3 horizontal mill that weighed about 8000lbs and I was wishing for more rigidity.
Less force required to maintain a heavy enough chip. Two flutes plunge better than four flutes. However since you're just reaming a 4 flute may work better so you'll just have to try both to see what you're machine likes the best.
Wayne Cook Shamrock, TX
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Reply to
Wayne Cook
I realize there are mills available better suited to this job. What I said was that they are not commonly found in a home shop.
I too have my concerns, which is why I posted the question. I'm not above saying that I can't do this job (actually, a favor for a friend).
I'm fairly certain there's not a single machine of that caliber anywhere within 30 miles radius of me. How far beyond, I don't know.
Thanks.
Reply to
DeepDiver
Thanks, that was very helpful.
When I wrote "job", I was using that term in the context of a "task", not a means of employment. I'm trying to help out a friend who's in a jam.
Reply to
DeepDiver
Just out of curiosity, how "clean" is the cut made by a plasma cutter? I don't think the edge finish would be acceptable to the final "customer". Furthermore, he would want a nicely-shaped round hole so that would mean a robotic plasma cutter.
Thanks
Reply to
DeepDiver
Why HSS instead of carbide? I bought some Atrax carbide endmills from Enco sale flyers and they are awesome in SS.
cs
Reply to
Chuck Sherwood
The problem with carbide is that if your set-up and machine are not rock-solid rigid, the carbide will fracture. HSS tends to be more forgiving.
- Michael
Reply to
DeepDiver
Agreed. And rock solid really means rock solid... Any chatter or movement at all - including simple vibration of the unit can ruin expensive tooling fast and furiously.
Another problem I've only read about is that Carbide tends to micro-fracture if coolant is needed but not used properly. The very tip of the carbide simply doesn't get cooled properly due to vaporization of the coolant around the area being cut, etc. Micro-fractures lead to not-so-micro fractures and then chipping, etc.
Regards, Joe Agro, Jr. (800) 871-5022
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V8013
Reply to
Joe AutoDrill
Take a piece of plywood and cut a nicely shaped hole in it somewhat larger than your 13/16th hole. Clamp it to the stainless and use it for a guide for the plasma torch.
Try to find someone with a plasma torch in your area and look at some of the stuff they have cut. Plasma is often used to make silhouette lawn art.
Dan
Reply to
dcaster
What I was saying is that there's a lot of home shop machinists out there with horizontal mills. They tend to be cheap so there's a fair number that get snapped up by people with the room for them.
I'm not saying you can't do it either. But I think you may be in for more grief and expense in tooling than the job is worth. That's a pretty tough job with the right machines. There's a chance you could do it with a mill drill but be prepared to buy a fair number of end mills and possibly have some other trouble as well.
For reference I bought that same machine at my former employers auction for $500 and then later sold it for $1000.
Wayne Cook Shamrock, TX
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Reply to
Wayne Cook
The interrupted cut is hard on carbide. Use M42 or M57 HSS, that's HSS plus cobalt. The M42, etc. is a LOT tougher than plain HSS, but also extremely tolerant of interrupted cuts, which the carbide has a problem with, especially when things are not rigid.
I have doubts about the Rong-Fu. I am pretty confident I could do this on my Bridgeport, although I'd probably have to baby it some to keep from trashing the cutters. I might try with 4-flute, as they are a little more rigid (thicker web) and you are not going to cut fast enough to fill the flutes.
Jon
Reply to
Jon Elson
I forgot you were in Texas where everything is BIGGER (including your home machine shops, I guess).
Seriously, I didn't realize that these machines were popular among home machinists; I thought they were prohibitivly large. Everyone I know who works in a home shop uses some form of vertical mill.
I realize that. I'm still not sure if it's feasible myself. I'm hoping the job doesn't require moving the center of the holes. Simply enlarging them was the original proposal and I'm fairly confident I can do that. If the holes do need to be re-centered, I may just pass on the "job".
Sadly, the liberals and lawyers have driven most of the big manufacturing industry out of California. So my choices are more limited.
Thanks again for your feedback! Michael
Reply to
DeepDiver
True. :-)
Not all horizontal mills are large. Even the small ones are more rigid than many vertical mills. I can remember dozens of people who are either on this group or have been on it that have horizontal mills. Some have added vertical heads to them to make them more versatile while other mills like mine are combination horizontal and vertical.
Agreed though I still have the speed concerns we discussed earlier.
That's funny. I'm always envious of you guys living in California have such easy access to cheap machines. Machines in this area are extremely scarce and normally bring premium prices because of this.
Seriously I see more machines available in California and the East coast when I look on ebay than any other place.
Wayne Cook Shamrock, TX
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Reply to
Wayne Cook
I think Horizontal mills are gaining popularity. I know a couple hobbyists that own them. One added a bridgeport M-head so that he can use it as a vertical mill two. I personally own two horizontal mills and I find them very useful machines.
chuck
Reply to
Chuck Sherwood
But as soon as you switch to end mills (per the the OP's requirement), you lose a lot of the horizontal's rigidity. I.e., the cutter is no longer supported at both ends. Bob
Reply to
Bob Engelhardt

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