Best way to build this part

[Chris64]

I'm trying to build a part. I've been able to do each cut individually just to prove the concept (small parts).

Part of my biggest concern is the very small size of the part. It only measures about 1/2" high x 3/8" deep x 1/4 wide. The bearing carrier is only 7/32" in diamter. The holes on the top and bottom are only .04".

Here are my planned methods (that follow along with the picture). My CNC doesn't have a 4th axis or an auto-tool changer so I'm trying to do this whole process with the least amount of tool changes and material rotations. I need to eventually make a few hundred of these (if it works) so the most efficient method would be preferred.

step 1) drill 2 .04" holes
step 2) 3/16 2 flute HSS mill. rough cut the profile (overcut .01), each Z axis step is .05 inch (five steps total)
step 3) finish cut along whole profile. I don't know if this is the best way to do it but with my experimentation it came out pretty nice looking
step 4) Rotate block, drill 3/16" hole all the way through. I know a drill bit would be best here but I'd like to still use the mill bit so I don't have to change the tool.
step 5) Helical cut up top for a bearing.
step 6) Flip part over and cut other side for bearing.
step 7) Rough cut the other profile shape using the same rates as step 2
step 8) Finish cut as in step 3
step 9) One more turn of the part. Rough cut slots until only about .05 remains on the bottom. Enough to still hold the part fairly rigid but can be easily cut off.
Step 10) Finish cut the last face at full depth. This will leave a small spot (when the part no longer has enough material to hold up to the cutting) that will need to cleaned up by hand but I couldn't think of anyway to avoid this. I'm sure the correct answer to this is to hold the part somehow, but I couldn't think of anyway to do that.

excuse the pics as I don't have a CAD program. I would like any suggestions to know if I'm planning this correctly.

Thanks.

[widgitmaster]

Can't get any more basic than that!
To get that much detail in only a few step is good planning!

Eric

[Chris64]

Well I guess that's the fewest steps possible. I was just checking before I start building a jig to hold everything. I figured I could have 2 or 3 stations in continuous rotation except for those two little holes.

Speaking of...any suggestions on the .04" holes? I could only find drill bits small enough in a hand-held pin-vise set but it broke when I was trying to make the first part. I found a place online that sells small drill bits so I think that part is covered but I tried to peck drill in .08" increments and it broke on the third stab. I tried again with another bit in one continuos run and it made it all the way through. Any recomendations for this?

[Chris64]

OK...I'm close.

I built the part just as described. It worked pretty good BUT because the part is so small I can't think of a way to hold it so I have to hold the stock side and just cut the part off. The problem is that it leaves a small spot where the radius couldn't finish the cut.

Are there any traditional methods (or better methods) of dealing with this? If you can't clamp the final part, how do you typically get a clean cut to remove it? I thought about trying a slitting saw but It would be too difficult to position the material vertically. I have a band saw but the finish isn't nearly clean enough for this (or accurate). I want to avoid manual clean-up as much as possible.

[BobWarfield]

What about this:

1. Bore the 2 side holes in each piece by laying the plates horizontally in softjaws in a couple Kurt vises. Alternatively, you could clamp to a fixture plate, but the vise setup seems really fast. Use a workstop on the left hand vise to start indexing the plates.

2. Flip the plates vertically in the vises to bore the holes and profile the sides. Don't try to cut them apart, just get that side profile done. Use two Kurt vises to hold the plates. They should set up and profile real fast. You can either try to back bore, or flip the plates to get the bores right before profiling. You will need a way to index in the vises, but a workstop should be adequate. You need adequate waste at the bottom of the plate to give the vises something to hang on to.

3. Clamp the plates horizontally on a fixture plate that has cavities contoured to hold the side bulges. Set up an index pin so you get it index properly and clamp by bolting through the side holes to your fixture plate. Now you can mill out the edges and the individual parts are held by the side holes, so you can get a clean pass on them. In order to keep the production line running smoothly, you may want to arrange to clamp your fixture plate for this operation in the two Kurt vises.

Best,

BW

[Chris64]

Originally Posted by BobWarfield 3. Clamp the plates horizontally on a fixture plate that has cavities contoured to hold the side bulges. Set up an index pin so you get it index properly and clamp by bolting through the side holes to your fixture plate. Now you can mill out the edges and the individual parts are held by the side holes, so you can get a clean pass on them. In order to keep the production line running smoothly, you may want to arrange to clamp your fixture plate for this operation in the two Kurt vises.

Thanks for the suggestions. That's one of the idea's I was considering. The side holes are REAL small so using them for mounting isn't really an option (#60 drill I think...around .04" diameter). But that top piece may be enough to clamp on to (around 1/8 of flat space before the bearing bevel).

I was thinking of cutting a block of alum to hold 4 of these side by side. Each for one of the position changes. Then I could run a program that cuts all 4 in one process...then I would move everything one step down on the assembly and start the run over again.

I also read idea's about leaving a couple tabs a few thousands of an inch thick and then just cutting it off with an exacto blade. It's manual labor, but the clean up should be minimal.

[BobWarfield]

I wondered how small the holes were. Pity.

Next thought would be to arrange the workflow so the pieces are held in soft jaws contoured to the bottom, much like the fixture plate described. Cut slightly over halfway down on top, flip to drop into the contoured jaws, and cut the rest of the way. The jaws will hold onto that lower half so it doens't move. Depending on the side of your parts, you can potentially cut more than one per vise loading. This could be one of those where you want four vises on the table to work with.

Best,

BW

[Geof]

How many of these parts are you going to make? If you are doing a few tens then stick with the tedious one by one approach more or less as you have outlined. A few hundred could be best approached by Bob's first suggestion but if you will be doing thousand then Bob's second approach with custom jaws is the way to go. When you are in the thousands an improtant thing is to avoid having to clamp each part individually into a fixture. You must figure out a sequence which takes a piece of stock equivalent to 10 parts and loading it with a single action.

[Chris64]

I'd like to make about a thousand of them to start with. I'm being optomisitc about the potential market.

I understand the logic of what your saying (10 parts loaded in a single action), I just don't know how I could actually do that.

My thought was to make a jig where the stock would fit and use something like this:http://www.newmantools.com/bowes/bowhor.htm to clamp it down so it could be quick and easy. Right now I'm just using the generic universal clamping set-ups from Grizzly.

In large quantities it probably makes sense to run-off a thousand of step 1, then a thousand of step 2...but to keep material waste to a minimum my plan was once a final piece was cut-off I could then just slide that same stock up and cut another one. I suppose I could do that by just using 10 full length pieces of stock all set up for each step. The nice thing is that the stock is 5/16 square so I could make the jig just 10 5/16 channels.

BTW, I should mention that I don't have a vice and I'm on a shoe-string budget. I'm suffering from a slight case of "wife"...I have to show some revenue before I'm allowed to spend anymore. That being said, any suggestions on a budget method of clamping down 5-10 pieces of metal in a single action? Or, if I had a Kurt with soft jaws (Not really sure what those are, just softer metal, right?)...how could I do it then?

[lerman]

Consider doing a bunch at a time. Take a long length of stock. Drill the small holes, turn it, drill the large holes, face the bearing seats.

You now have a piece of stock with all of the holes for ten or twenty parts. Now rotate the stock so you can do the "bottom" -- I think of that as the part where the large holes are perpendicular to a flat with "wings" going up. Do all of the parts. Also, do the top, but keep the parts connected by a strong pridge.

Now you should be able to place the parts on a fixture consisting of ten vertical pins. Clamp them down and do both sides.

Turn the fixture sideways now and carefully mill off the "bridges".

Ken

[Geof]

You have the classic problem of an entrepreneur; too much optimism and not enough capital. Still optimism is good thing and ingenuity and hard work can compensate for lack of capital. Here is how I would approach this problem.

I have shown a cross section of the fixture I would make. The red block is fastened to the machine table and has two dowel pins and two threaded holes for the bolts that attach the blue block which is the body of the fixture; these bolts and dowel pins are not shown. The blue block has dowel holes in faces 1, 2 and 4 and has holes for bolts to attach it to the red block on either face 1, 2 or 4. 3 will be mentioned later. The green block is a clamp to hold the stock (pink block) using bolts located adjacent to where each part will be machined. Notice the clamp is relieved on either side of the clamping bolts and also in the root of the lip that clamps the stock. This is needed for efficient clamping particularly for the stock which would only be held at the bottom corner due to deflection in the clamp if this relief was not there.

Obviously the stock held within the clamp cannot be machined. Very often it is more efficient overall to use material that has excess size simply because this makes clamping possible. The material cross section needed for the part is shown approximately by the black rectangle drawn in the pink block.

The base and body would both be machined out of hot rolled mild steel and the clamp cold rolled mild steel.

The machining sequence is best described by referring to your picture. You show the first operation as the two very small holes and the profile around them. These holes and the full profile, full depth, would be done with the fixture holding the stock as shown in the picture; face 1 bolted to the base.

The body of the fixture is repositioned with face 2 against the base and the profile and bearing hole shown in the right hand part on the second line in your drawing are done. This time the profile is done just past the mid point.

The partially machined stock is taken out of the fixture, the fixture body is attached to the base by face 4 and a filler piece cut from a length of the stock is put in the stock clamping location and the clamp bolts tightened.

Now the inverse of the profile done in the second operation is machined into the joint plane 3. After this is done a few thou are machined off the clamp face so the clamp will close firmly on the profile not just on the unmachined faces.

The partially machined stock is now clamped into the profile sockets and the parts are fully machined and at the same time separated. Further up I mentioned that the clamp has a bolt adjacent to each part location. This is so that when the final operation is done each individual part has its own clamping bolt and is held firmly even when separated.

If I wanted to economize on material I would not machine away all the excess but would do operations one and two with faces 2 and 4 against the base. Then I would remove the stock which now has parts along both edges, split it along the middle on a bandsaw and then finish machine and separate the parts from the two halves.

[Chris64]

OK...first off, thanks everyone for your replies. I'm really thinking about all of the suggestions and trying to think of what will work well (given the small scale...and my budget).

Here's what I'm thinking. A single jig that could hold a handful of stock. They could be held down in pairs so fewer tightening actions. I was planning on putting a spring under the clamp so that when it's loosened I could easily take them out or rotate them (the angle cut directly above the spring is so that they will hold somewhat straight when removed and retightened). The fitted channel will help hold the small stock so it doesn't deflect too much. I was thinking about putting a channel in the front edge that I could slide a temporary piece of stock to use as a stop for the front edge of all the material. Do you think this would give consistent enough results though? The only real concern about consistent is for the two bearing holes...these have to be perfect.

I'm still trying to decide the best way to deal with the final cut-off. Possibly a custom vice that could slide into the bump stop slot. Or perhaps a custom jig just for that procedure. Then I could be loading parts into that while the other cuts are in process.