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Countersink problems
Posted: Mon Dec 10, 2012 11:10 pm
by saminmn
I am having a problem driving screws flat or below the workpiece surface. I am making a jig to aid in cutting sheet material. The circular saw will ride in a cradle or base that will follow a track clamped to the sheet. So the cleats and other pieces surrounding the circular saw are attached to the base with countersunk flat-head screws. The first set of screws comes up through the 3/4" base into the 1 1/2" thick rail that rides on the track I drilled the countersinks first then holes in the birch plywood and smaller holes into the maple rail. When the Number 12, 1 3/4 screws get most of the way in, the drill bogs down. I tried going to a size larger bit, got farther. I tried drilling the countersinks a little deeper, maybe a little deeper. Used manual screwdriver to try to finish driving. After considerable effort I have gotten 3 of 4 screws flush or just below the surface. the forth screw has broken off and I will be starting over on that one. I am looking for advice. I think maybe the countersinks and shank holes are not exactly aligned and the screw's beveled head is hitting one side of the countersink early. At first I did need to go one size bigger on the down hole bit (I think that if I go a size larger still, it will strip out) and I dropped a smaller bit into each hole to measure and ensure that I was at the full depth for the screw's length. The countersink bit I am using looks to be no larger around than the screw head, so there is no slop to get the screw below the surface. My prior experience with countersinks is in cheap plywood mostly and a little force could draw a head into the plywood
Anyway, specific questions are, should I get a larger (than #12 screw head) countersink bit? Are the all-in-one countersink/tapered screws the way to go and if so does it need to match the screw size/length closely? Is there a guide or general guidance for the bit sizes to use for a given screw size/wood type? Maybe I need to see if a next larger bit size will in fact strip out in my 1 1/2" maple.
This attaching this first board has been a pain and I have 3 other sides to hold the saw in the base.
But, not such heavy screws there.
Thanks in advance for any help.
Posted: Mon Dec 10, 2012 11:49 pm
by beeg
Did you use the counter sink in a drill press? Did ya drill a pilot hole? Wax the threads?
Posted: Tue Dec 11, 2012 7:49 am
by pennview
Here's a chart that gives you the information about what size drill bit to use for various sized wood screws, along with the correct size counter sink to use --
http://www.wlfuller.com/html/wood_screw_chart.html
Note that if you are using traditional wood screws, not drywall screws, you typically need to use two different drill sizes, one to match the diameter of the shank and a second one to match the screw's root diameter (or use one of those tapered drill bits). Also note that which size drill bit you'd use to match the root diameter depends on whether you're drilling into hardwood or softwood.
Posted: Tue Dec 11, 2012 11:48 am
by saminmn
beeg wrote:Did you use the counter sink in a drill press? No Did ya drill a pilot hole? yes. one for shank and smaller one for actual pilot Wax the threads?no - never heard of this
I was not in drill press mode and did not realize I needed to go to it, if that is what you are telling me.
Was easy to grab cordless drill and just swap bits around - except it did not work out easy.
Posted: Tue Dec 11, 2012 12:00 pm
by saminmn
pennview wrote:Here's a chart that gives you the information about what size drill bit to use for various sized wood screws, along with the correct size counter sink to use --
http://www.wlfuller.com/html/wood_screw_chart.html
Note that if you are using traditional wood screws, not drywall screws, you typically need to use two different drill sizes, one to match the diameter of the shank and a second one to match the screw's root diameter (or use one of those tapered drill bits). Also note that which size drill bit you'd use to match the root diameter depends on whether you're drilling into hardwood or softwood.
Thanks for link:) It is what I need I think. I don't know how to know what size my countersink is. But, I had not thought of doing a counter-bore to make sure the head is down and not going to be in the way
Posted: Tue Dec 11, 2012 12:01 pm
by JPG
The fact that excessive torque is needed to get the screws 'in' indicates the pilot hole is too small. Maple is quite unforgiving of that.
With hardwood, the screw head will not compress it like plywood.
Since there are two pieces, does the piece next to the screw head have a clearance hole?
If using dry wall or cabinet screws(hardened) breaking off is common.
The pilot hole should be no smaller than the root diameter of the thread.
P.S. A hand drill is a PP way to create screw holes.(not vertical, no depth control?, odd shaped holes. . .).
Posted: Tue Dec 11, 2012 12:05 pm
by beeg
The reasoning about asking about using a drill press is that it wood insure that the hole is straight and maybe a little bit better control on the depth of the countersink hole. I use a little bit of beeswax to help drive the screw and it helps to keep it from snapping off.
Posted: Tue Dec 11, 2012 4:44 pm
by berry
pennview wrote:Here's a chart that gives you the information about what size drill bit to use for various sized wood screws, along with the correct size counter sink to use --
http://www.wlfuller.com/html/wood_screw_chart.html
Note that if you are using traditional wood screws, not drywall screws, you typically need to use two different drill sizes, one to match the diameter of the shank and a second one to match the screw's root diameter (or use one of those tapered drill bits). Also note that which size drill bit you'd use to match the root diameter depends on whether you're drilling into hardwood or softwood.
Thanks for that link Art, I've managed to Bookmark It, and I'm sure I'll return here from time to time. What a selection counter sinks they have!
Posted: Wed Dec 12, 2012 1:42 am
by saminmn
JPG40504 wrote:The fact that excessive torque is needed to get the screws 'in' indicates the pilot hole is too small. Maple is quite unforgiving of that.Yes, according to the link provided by pennview my shank hole should be 7/32 and the pilot 5/32. I am going to use the sizes on the replacement for the broken screw.
With hardwood, the screw head will not compress it like plywood.
For this first board, the countersinks are in birch plywood. I just used calipers on the countersink. The one I own is .374 (3/8) inch. The head of the screw is .42. So, it is a little smaller than snug.]
Since there are two pieces, does the piece next to the screw head have a clearance hole? yes, but by the guidelines they are too snug. when I do a new hole for the screw I will use 7/32" bit per the guideline for #12 shank hole, if I read it right
If using dry wall or cabinet screws(hardened) breaking off is common.
The pilot hole should be no smaller than the root diameter of the thread.
Again, If I read it right, the guideline says 5/32" for pilot.
P.S. A hand drill is a PP way to create screw holes.(not vertical, no depth control?, odd shaped holes. . .).
Well, I wanted to drill all the holes with the boards in the same position relative to each other, so I clamped them together and put them in my vise with the under side of the base facing up. I was not too concerned with vertical or depth of cut, as long as all holes made used the same setup. I did not have any idea I would run into problems and using the drill press would have required me to think of some way to assure that the holes would line up exactly between the boards.
Thanks for the comments. Is there some way that is standard to get needed hole match-ups in drill press mode? A thought that came to me while thinking on it now is to drill through both workpieces at once using double sided tape hold together instead of clamps.
Posted: Wed Dec 12, 2012 1:54 am
by JPG
saminmn wrote:Thanks for the comments. Is there some way that is standard to get needed hole match-ups in drill press mode? A thought that came to me while thinking on it now is to drill through both workpieces at once using double sided tape hold together instead of clamps.
If possible, drill one hole in both pieces. Screw them together. Drill a second hole and install second screw.
Drill the rest of the holes, then insert screws.
I usually drill all pilot holes and 'pin' the first two holes, then enlarge/countersink the outer piece.
I rarely use a hand drill. if drill press(hor or vert)can be used.