On 2009-09-06, Ignoramus11113 wrote:
On 2009-09-06, DoN. Nichols wrote:
On 2009-09-06, Ignoramus11962 wrote:
[ ... ]
I have only one plate (but want to make the missing ones). I am pretty
sure that on my plate there is a number divisible by 3.
O.K. Do you need the order in which the holes are present on a
typical set of plates? My head is also a 40:1 head, so it will give a
good starting point.
I would love to get that info, indeed. Possibly different sets have
different counts. Let me know, this would be great. I will buy 6" 1/2"
thick disks at mcmaster and will drill them.
O.K. From my B&S one, which has somewhat smaller plates
(largest number of holes is on the outside row):
Plate #1 #2 #4
Row == == ==
Outer 20 33 49
19 31 47
18 29 43
17 27 41
16 23 39
Inner 15 21 37
The apparently missing ones are multiples of smaller ones or
divisions of larger ones.
1 Any disc and row
2 Any even row on disc 1
3 15, 18 on disk 1
21, 33 on disk 2
39 on disk 3
4) 16, 20 on disk 1
5) 16, 20 on disk 1
6) 18 on disk 1
7) 21 on disk 2
and so on.
My plates are 5" diameter, and about 1/4" thick. (0.243, 0.245,
and 0.247")
If your existing plate is 1/2" thick, remove it and check the
other side. It may have a different set of holes there, with the holes
all going only half-way through (except where two line up by accident).
This brings up another question, that I would probably ask in a
different thread. The thinnest steel round disks at McMaster are 1/2"
thick.
And what is the thickness of the plate on your index head? If
1/2", check whether they are doing the trick of flipping it over for a
second set of holes. If not -- prepare to turn it thinner -- perhaps
after drilling. Or -- get some 1/4" steel plate, lay out circles on it,
bandsaw to approximate diameter, and turn on a faceplate with a live
center clamping it (and something to spread the force to out near the
edge). Obviously -- put a sacrificial spacer under the workpiece so you
don't turn the faceplate.
I will need to drill several hundred holes in 1/2" steel disks, and I
would much prefer to do that in one operation, as opposed to starting
holes with a center drill and then drilling 1/8" holes.
Understood.
To that end, I looked up screw machine drills at McMaster, hoping that
they are short enough to not wander without center drilling. It would
seem that the 1/8" screw machine drills can drill 0.68" holes, so they
ought to be enough for drilling 1/2" plate.
Most screw machine bits are also ground as split point. Split
points wander a lot less than the standard chisel points found on most
jobbers length drills. When drilling a flat plate, I think that you can
do fairly well here.
I may try to use a screw machine length carbide drill, so that I would
not need to worry about lubrication and drill at high speed so as to
waste less time.
Hmm ... you need really good fixturing with the carbide bits.
Any slip to the side and "plink" -- a broken bit.
But -- this means that if it *does* wander, it will break
instead of drilling a hole off location.
Do you think that item 27515A11 would be able to
drill steel without center drilling? (in a Bridgeport)
It has a split point, which is important. They are expensive,
but I would suggest that you get several, since it will otherwise bring
your project to a halt if the bit breaks. And carbide *does* break
easily.
What spindle speed can you get?
How will you hold it? Collet, drill chuck, end mill holder? If
a drill chuck, how much runout at 1/8". (BTW -- you did check the hole
size in what you have I presume. IIRC, my B&S one is closer to 0.100"
holes. But I've never had to drill a new plate, so I could be wrong.)
But if the holder has a short enough overhang and has minimal
runout, if the spindle speed is high enough, and if the power feed is
slow enough, then it could work quite well.
Are you planning to use your perl script to make a list of hole
coordinates? You might consider using the index head itself to drill
the circle of holes. Which set of holes do you have? Can you use them
with the chart to make the other hole patterns you need? It will give
you good practice using the dividing head and the sector arms. Just
rotate it until the spindle faces up instead of horizontal. You can
divide a temporary plate by hand or using your rotary table, and use
that for drilling the hole circle you need. Note that the 40:1 ratio
means that your placement errors in your temporary plate are reduced by
a similar ratio.
Good Luck,
DoN.
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