Model Engine Maker
Help! => Specific Engine Help => Topic started by: Davis2x1 on August 14, 2015, 02:09:51 AM
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Trying to finish up my first steam engine. Most machining worked out relatively well except for cross drilling across a gap as in a clevis. I can locate and center drill "OK" but when I try to drill the hole, the top side is straight but when the drill bit hits the lower surface the location wanders and I get an off center hole. The clevis pin is now crooked
Would placing a filler in the gap keep the hole straight?
Thanks for your help. Dave
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Dave, a filler would help as long as it is held securely in place and can't move itself. Another way would be to drill through the top hole with a smaller center drill or spotting drill, thus making a dimple in the bottom surface to keep the drill in line.
Bill
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Dave,
It may be academic now but another way to "drill" it is as Dave said center drill it undersized but instead of a drill if you have it use the appropriate endmill size, that won't walk.
Art
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Dave....in full size cylinder clevis work, we would install a size for size spade, add a few substantial weld tacks so the three elements are one, then drill/bore to the required clearance to suit the clevis pin
In reality for model work, the same process would seem appropriate...
If the clevis lugs are currently drilled/bored off axis, the same process could be employed in oversize boring the clevis lugs, bush & then repeat the process to return correctly aligned correct size pin holes......Derek ..... :cheers:
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One way is to center drill each side from the outside to what looks like, or is scribed to center of the partial circle.
Drill a hole in block of material and make a center that will fit hole. Center will be aligned with drill press or mill spindle now.
Put wood or plastic spacer in clevis gap so it don't want to spring down with drill pressure.
Clamp with bottom on center and center on top aligned with drill bit.
Go slow when drill wants to start in second half of clevis. Remove center, align on drill bit and clamp in place to finish.
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Go slow when drill wants to start in second half of clevis.
As Gary has mentioned already. Does the drill has, which you have used for this operation, a proper grinding ?
If the drill bit is new and you start the drilling with some carfull spotting into the second half, it should work.
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Its a bit late to mention now but I normally drill before I machine the slot in the end ;).
Jo
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Its a bit late to mention now but I normally drill before I machine the slot in the end ;).
Jo
+1
Or if the hole is above 1/8" get yourself a long series centre drill to spot the second hole after drilling the top one to suite the ctr drill shank
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Jo's answer is the best solution. I spend a great deal of time trying to think through the "best" sequence to a series of operations on a part. This generally begins with "what can go wrong?"
One issue is drilling through air as across the clevis slot. As in Jo's answer, not having a space eliminates this. In addition, it elimates having to file away the drill burrs on the inside of the slot.
Of course, we never think of these things until it's too late.
That said, on small holes (smaller than a spotting drill), I drill the first hole and then use a tiny brad through the hole as a transfer punch. The pointed end of the brad is held in position with tweezers and tapped with a small hammer. Then the drill will have a guide pop to keep it in position to finish drilling the second hole.
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+ 3
For Jo,s method
Stuart
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Thanks for all the tips. I guess I have to think about the machining sequence a little more. Drilling before cutting the slot appears to be a good method. After having drilled an offset hole on the crank shaft bearing, I did use Gary Harts method of boring each side independently. This worked fine.
BTW the engine is a PM #5 Coke Bottle.
Thanks again, Dave
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Any chance of seeing some pictures of your progress so far Dave?
Bill
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Attached Photos.
First photo shows first fit-up of the valve assembly.
Second photo shows con-rod clevis that needs rework.
Dave
P.S. Third attempt.