Depth of Vent Lines

[deltaenterprizes]

I am working making a couple of molds and plan on putting vent lines on the face of the blocks. Any idea of how deep they should be?

[theperfessor]

When I made mine I cut the lines 0.006 deep and 0.100 apart with a tool that had a sharp 60* point, similar to a threading tool profile. Seemed to work OK. Some people use a flycutter and a rapid mill feed to create a series of overlapping circular grooves, similar to Lee's 6-holers. I like straight lines and smooth faces as it makes any lead that sticks to the faces much easier to remove and allows recutting with a thread file if more venting is necessary.

Not criticizing anybody else's methods just like to do it the old fashioned way.

Both work well if done right, just my $0.02 worth.

[deltaenterprizes]

Thanks, I plan to use the same spacing but I was not sure of the depth. A 10 TPI junk tap would be a nice tool to do this job but I guess I will have to make a tool on the lathe to do it in one pass.

[44man]

I make mine .002" with a fly cutter. Vents good. I also use a 60* cutter. I don't like larger because of whiskers. I ladle cast and large vents leak too much.

[leftiye]

Anything that leaves a gap of .001 between the faces will work. Lotsa air can leak out of a small hole. Ironically, a much larger gap may (.003" in my experience) not cause any fins on your castings. As in a beagled mold. Gotta admit that grooves look better.

[theperfessor]

deltae-

I thought about using 10 TPI tap also but the rounding of the crest was so great that I rejected that idea. Have finished plans and am halfway through building tool to cut multiple grooves at one time. If your interested I can send you 3D DXF file, which should open in any compatible CAD program (AutoCad, etc.)

Wish you success in your efforts.

Leftiye

That why I use a 60* V and cut grooves in one side only. Leaves plenty of room for air to escape but maximizes surface area of passage to stop lead flow due to lead's higher surface tension. I understand this may not be enough for pressure casting, but it seems to work fine from a bottom pour using all the alloys I've tried.

[jhrosier]

... Have finished plans and am halfway through building tool to cut multiple grooves at one time. ....

The tool in the pictures is not going to work well.
To use that style insert, the cutting edge needs to be on the centerline of the holder and the slot needs to be cut at an angle to provide relief for the trailing edge of the insert.

Something like this:

http://images42.fotki.com/v1447/photos/5/590147/2786028/cutter-vi.jpg

Notice the relief on the top of the insert also.

hope this was helpful.

Jack

[leftiye]

How about a roughing (or plain) endmill with grooves ground in the circumference? Cut air vents with a side milling technique (vert. mill). Or, you could use a threading cutter to groove a piece of O-1, and then mill flutes in it, and then heat treat.

[theperfessor]

jhrosier

I see where you're coming from. I posted the wrong CAD file of the insert. Maybe the correct file as posted below might clear things up. The insert is to be made from 1" diameter A2 rod. The concentric rings will be cut on .1" centers with a 60* threading tool to a depth of .087" to leave a sharp point on the OD. I plan on cutting about 6" of rod at one time. The rod will then be clamped in the 3-jaw chuck on my dividing head and supported on the off end with a center. Mill the insert to 1/16" below center, flip 180*, and mill other side to leave insert about 3/16" thick. Cut into 1.4" lengths. After quench hardening and tempering the insert will be ground flat on surface grinder.

When clamped into 3/8" wide slot in tool holder this puts top surface of insert on center and will provide 0* face relief and about 7* end relief. This is identical to the single point tool I am currently using to make grooves one at a time. Insert can be flipped around if it gets dull.

The hole in the tool holder is designed to allow a brass rod to be used to push insert against vertically oriented face of mold block before clamping insert into place. This should allow for a uniform depth of cut across mold surface.

[jhrosier]

Ah! now it makes sense.

If you have more money than time, you can buy thread milling holders and inserts from Seco.
The finer pitch ones might have the shape that you are looking for.

Jack

[theperfessor]

Jhrosier

Yeah, I checked out thread milling inserts but in the required pitch the points have too much flat on them and I don't really want to go to a finer pitch to get a sharper point. I figure that by making four inserts at a time and with two cutting edges I should have enough to cut a lot of mold faces before retooling, plus the ability to grind worn insert slightly thinner and shim up under bottom for even more use.

It will also makes a good demonstration project to show my students heat treating and surface grinding so I don't mind putting in the time.

Thanks for thoughtful comments.

[Greg5278]

The best, ans easiest way to cut vent lines is with the surface grinder. No not the hand held type. A precision ground band across the mold faces will vent air, without allowing "finning". I use the method, as do some custom mold makers. The cuts should be .00075 to .001" per side. The alloy will not flow into such a small space, even with 30-1 or Linotype. The added bonus is that the lines do not clog up like milled grooves. A milled groove tends to pick up flakes of lead, and resudue which lessens the venting effectiveness.

A regular wheel can be used, and the band width is adjusted depending on caliber. I usually have one band of .250-.375" wide for 750gr .730" diameter molds, but needed 3 bands on a 1043gr .730" one. The larger slug required the one band to be paralell to the bullet cavity, and perpendicular to the other lines.

Greg S

[theperfessor]

greg s-

Are you using that on steel molds or aluminum? Any problem with wheel clogging on aluminum?

Makes me sorry I sold a little South Bend shaper I used to own, it would make all this unnecessary. Anybody have a small shaper for sale at a reasonable price?

[Greg5278]

The aluminum doesn't seem to clog the wheel as long as you run coolant. A coarser wheel does fine.
Greg