Flat bottom holes.

mikey said:
You don't mention your tolerances. If the hole has tight tolerances, has to be straight all the way down the bore with a good finish and a really flat bottom then boring it would be the best way to do it. Given the depth and closed bottom, you are looking for a positive lead solid carbide boring bar.
Click to expand...
Bore diameter tolerance is quite loose because I can make an appropriate size piston to fit the bore.
 
Last edited:
A simple hole like that would take a few minutes and you're done. Reamers are okay, too, but you have to size the pre-reamer drill so the reamer has to only remove about 0.005" or less if you want accuracy and a good finish. And your drills need to be sharp. Then you need to flatten the bottom.

For me, I would just buy a Micro 100 boring bar, drill an access hole and bore it. On size, straight walls, fine finish, flat bottom.
 
As discussed previously, the problem with using an endmill would be finding one of the correct diameter to use with the reamer.
If it were me, I would use the correct size drill bit to make the hole, then when the leading tip of the drill bit is at the correct depth, grind the end flat, then sharpen the flattened flutes like an end cutting endmill. Go back in and take out the cone at the bottom of the hole. Then ream to final dimension.
 
I am surprised that my OSG cutter cuts undersize (.243) but cut depth is too short. I hope a long reach endmill does also.
 
I would drill with drill a little smaller than 1/4 dia then use 1/4 dia flat bottom drill to finish To depth.
 
The hole will have to be bored or reamed to get the finish needed for a cylinder wall. Boring will get a flat bottomed hole. A conventional reamer will leave a small chamfer at the bottom of the hole even if the hole were flat bottomed before reaming. A D-bit reamer can give a good finish and a flat bottom. Ideally you would want a chamfer at the open end of the cylinder to aid starting the D-bit. Allow a little sacrificial material at the open end of the cylinder for the chamfer. Machine it away after reaming.

As a practical matter a little extra clearance space at the end of the cylinder will not matter.
 
While not familiar with your particular kit, I am aware that most steam engines have the cylinder and the "head" as seperate pieces. A quarter inch bore isn't much, but the small screws are available. Would such be an option?

.
 
A separate head held by screws seems like a viable idea.
George H Thompson describes D-bits in his book. I believe Clickspring had one or more videos on the subject.
 
You must log in or register to reply here.
Back
Top