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DickDastardly40
12-16-2011, 12:47 AM
I have 40 metres of 316 SS track in 12 sections of up to 4 metres long with holes at 100mm pitch currently for M6 clearance which I have to drill to M8 clearance.

The sections of the track is T shaped and is 14mm thick counter-bored to take a cap headed screw so the actual thickness needing opening out is about 5mm. The bottom of the counter bore is countersunk.

I have only a basic drill press to do this as well as cobalt drills and spray coolant.

I am intending to drill through from the counter-bored side but foresee a lot of burring where the drill breaks through, on any other material I would consider using a countersink to deburr but have always experienced a lot of chatter on SS.

I guess I should just have at it and see how bad it it gets, but was wondering if anybody had any good ideas for minimising burrs or cleaning up the holes afterwards.

lakeside53
12-16-2011, 01:47 AM
Use a countersink, but get a zero or single flute version. No chatter, easy to control.

Like these (ignore the prices...)

Zero : http://www1.mscdirect.com/cgi/NNSRIT2?PMAKA=45117470&PMPXNO=8581081&cm_re=ItemDetail-_-ResultListing-_-SearchResults

Single : http://www1.mscdirect.com/cgi/NNSRIT2?PMAKA=01053248&PMPXNO=1676242&cm_re=ItemDetail-_-ResultListing-_-SearchResults

Paul Alciatore
12-16-2011, 02:42 AM
I would drill with a standard 8mm drill to enlarge the holes. Then I would use the 8mm step on a metric step drill to debur the holes. Step drills have a small radius or angle at the inside corner of each step and they do an excellent job of deburing holes. You may even find one with a large enough step to allow drilling and deburing in one operation. The trick which makes this great is using the depth stop of the drill press to set the depth for the step drill. This makes every hole the same with a very precise adjustment of exactly how much you take off. The diameter of the 8mm step will do a good job of preventing chatter so you can just slam it down and then up and on to the next hole. Do use a dab of cutting fluid every two or three holes. It should go very fast.

Another tip would be to use a piece of plywood or particle board to back up while drilling. It should be small enough so that the previous hole is past the edge of the board so the burrs created do not lift the track above the surface of the drill press which would cause the holes to be drilled at an angle.

DATo
12-16-2011, 09:11 AM
As I mentioned in another recent post on essentially this same topic, I've moved a lot of stainless steel in my career and the best method I've found for deburing those nasty exit sides of the holes is to simply use another drill about 50% bigger than the drill used to create the hole.

Turn the workpiece over and, if thin, lay it on a substrate of plywood or some other expendable material to keep the point of the drill from drilling into the table. Clamp a block or just about anything tangent to the workpiece to keep it from spinning in the event the drill grabs during the deburring process (but the part itself is not clamped down allowing for very fast movement to the next hole). While using a VERY low speed feed the oversized drill into the burr slowly after setting a quill stop to make sure it doesn't go too deep. You need to hold the workpiece down securely with your free hand to make sure the depth remains constant for each hole (the workpiece may have a tendency to get sucked upward into the drill though this happens very rarely. Once you get used to the amount of downward pressure you need to use on the quill this will not be a problem).

EDIT: You'll find that once you get used to the "feel" of this method of deburring you can move very quickly if you have a large number of holes to deburr.

GadgetBuilder
12-16-2011, 09:22 AM
Adding secondary point angles to the drill generally minimizes the exit burr. Worth trying to minimize the deburring effort. Also helps eliminate chatter as the drill enters an existing hole and in most materials extends drill life.

Picture:
http://www.gadgetbuilder.com/6_Facet_SplitPointC.jpg

Also see:
http://www.icscuttingtools.com/the-champ/drill_point_geometry.pdf