Vince's BP CNC conversion

[N4NV]

I have spent the summer hang gliding and did not have a lot of time to work on my mill. Now I have a littel more time available. I have the limit switches in place so I have increased the speed to 90 IPM. I have uploaded a video of the mill at 90IPM while running Art's road runner test program. I still have the backlash but have learned to live with it for now. I do have great repeatability though. After running the road runner programs (5 minutes and 30 seconds), my digital read out displayed 0.0000, 0.0000. Ocasionally it will read 0.0005 after running the program but never more than that even after running the program 4 times in a row.
http://www.flyingcritters.com/video/90IPM.wmv

Vince

[jdelaney44]

NICE! Hey, those motors are kicking ass! I may invest in new motors after seeing that.

Been off the machine myself. Taking some .Net courses that are taking all my time.

Best,
John

[snakebit95]

Video looks good. However, I would be really careful working around that machine with the handles spinning like that. You could easily end-up with a broken hand or something worse.

[RonGinger]

Did you put a ballscrew on the Z-axis? The photos look like you are just driving the crank-handle for the knee- did you do anything to reduce the gear-lash in the bevel gears?

Im doing a Jet knee mill now and I am driving the knee.

[N4NV]

I am just driving the crank handle shaft and turning the original acme screw and bevel gears. The weight of the assembly seems to keep out most backlash. In fact I believe the Z axis has less backlash then the other two axes that have precision ground ballscrews.

Vince

Originally Posted by RonGinger Did you put a ballscrew on the Z-axis? The photos look like you are just driving the crank-handle for the knee- did you do anything to reduce the gear-lash in the bevel gears? Im doing a Jet knee mill now and I am driving the knee.

[N4NV]

I decided to try tapping with Mach 3 today using a tapping head. Several months ago I purchased a Procunier size 3 tapping head on eBay for $90. At the time I had no idea how big a size 3 was. It turned out to be huge. I just put it in a drawer and forgot about it. Fast forward to this weekend. I decided to make a welding table out of a 35”x15”x1” piece of aluminum with holes drilled and tapped on 2” centers. I had made a similar plate for my mill while I was taking a CNC class and had use of a Haas CNC mill. This time I would use my converted Bridgeport. Due to the size of the plate I had to drill and tap it in 4 quadrants (after tig welding 20 holes closed that came in the plate and surfacing it).

I used a G73 peck drilling cycle for the holes and then just G1 and G0 moves for the tapping. The Procunier tapping head reversed at twice the RPM as the feed. I was running it at 210 RPM to it would reverse at 420. I have read that I should feed it at 95% of the calculated feed rate to account for any possible slippage or slop in the system. I used a forward feed rate of 15.2 IPM and a reverse at 30.4 IPM. The size 3 is so large that it took all but the last 1” of my knee travel to clear the table. I am always nervous any time I try some new program but everything went perfectly. The holes were drilled at a rate of 1 every 36 seconds and the tapping took 12 seconds per hole. There are 112 holes in the plate. I posted a video here:

http://www.flyingcritters.com/video/Tap.wmv

I know some people will cringe at using WD-40 for tapping fluid, but it works for me. The ½” tap I am using has tapped over 250 holes 1” deep and it still looks sharp.

Vince

[N4NV]

I'm talking about real cookies, the type you eat. I have had a bunch
of ideas running through my head about what uses I can find for my
CNC mill. I hit on chocolate molds, but I found I needed a flexible
mold to get the chocolate out. I then hit on the idea of using the
molds I made for making cookies. I first tried a batch of sugar
cookies but found that they rise too much and I loose the image on
the cookie. Spritz cookie dough will work much better since they
done rise much.

I first imported an image of our hang gliding club (a red tail hawk
holding a hang glider pilot) into Lazycam. I had Lazycam scan the
image at .01" grids X and Y and a depth of .1". I used a 1/2" 90
degree pointed mill to cut the nylon plastic. I was able to cut at
60 ipm. It took about ½ hour to cut one mold (about 2"x2.5"). After
the finished cut I cleaned it up and used a propane torch to smooth
the tooling marks a little.

To put the image on the cookie I dusted the mold with corn starch and
also dusted the bottom of a glass that I used to press the dough into
the mold. Gently peel off the cookie and bake until brown on the
edges, enjoy!

For all of you who have spouses that say you spend too much money on
your hobby, this is a chance to win them to your side.


The finished product waiting for the oven.

Vince

[BobWarfield]

Vince, I've been following your progress with keen interest. Thanks so much for keeping us in the loop.

On the tapping head, Wow! That's a big tapping head!

I had a friend recommend that Harbor Freight's head is actually decent, so I bought one new. Haven't had a chance to try it yet, but I will.

On the cookies--brilliant idea!

I would think you could make a cottage business out of custom cookie molds if you wanted to. Businesses and organizations of various kinds would love to have their logo on one. Or, you could just do a selection of interesting motifs and sell them on eBay.

Best Regards,

Bob Warfield

[wildcat]

Originally Posted by N4NV I decided to try tapping with Mach 3 today using a tapping head. Vince

Vince, Would you explain this operation a bit more please? I am just in awe of your video. I have never used a tapping head so I have no idea how they work in general let alone with a CNC machine. Do you simply position the tap, turn on the spindle, raise the table enough for the tap to penetrate, and then lower the table? Is this really all there is to it? The tapping head reverses direction when the table starts to lower? How do you calculate the feed rate? Is there some room for error on the feed rate, i.e. can the tapping head float up and down a bit to compensate for too fast/slow of a feed? What happens when the torque on the tap is too much? Does the tapping head stop turning in that case? Lot of questions but you are obviously the tapping man! Thanks!

[N4NV]

If you are going to use a tapping head in a CNC machine you must know what ratio the forward speed is to the reverse. The Procunier has a 1 to 2 ratio; it turns at twice the RPM on the reverse. All the tapping heads I know of reverse direction when you withdraw them. To calculate the fee rate you take the machine RPM/threads per inch. In my case 210 rpm/13 TPI=16.1538. You don't want the rate to be exactly as calculated because the spindle could slow as the tap enters the work. In this case you would force the tap into the tapping head causing damage. A useful fudge factor is 95%. So my down feed would be .95*16.1538=15.3461. I just used 15 ipm.

If the down feed is too slow the tap pulls down on the tapping head, the clutch disengages and the tap stops turning until the head catches up and the clutch engages. So there is no problem with a feed rate slower than calculated.

If the torque on the tap is too great the clutch will slip. If the machine is still driving down the clutch will not slip anymore and you will snap a tap.

Now, when you start to lift the tapping head the tap pulls down and causes it to reverse direction, even though the spindle has not changed speed or direction. The up feed has to be twice the down feed (in the case of the Procunier) so I withdrew it at 30 ipm. Because of this self reversing, tapping on a CNC machine with a tapping head can be faster than with rigid tapping.

Once before I have tried to hand tap a ½” hole in aluminum. It took at least 15 minutes. A tapping head did it in 12 seconds. I would highly recommend getting one. They can be found on eBay for under $150. If you buy one, make sure it covers the tap range you have in mind. I have two of them, one a size 1 and the other a size 3. With Procunier, that will cover from #6 up to ¾”.

Vince

[wildcat]

Most of the holes I tap are in aluminum in the range of #4 to 1/4. I normally use Cleveland 2 flute spiral point for through and spiral flute for blind holes. Would these be suitable for use in a tapping head or are different taps needed? Is it safe to use these small taps in a tapping head? I wonder about keeping the chips and flutes cleared moving from hole to hole. Broken taps are really disappointing.

[N4NV]

I have not tried anything as small as #4. If you are worried about chips you could peck tap it. I did several of my 1/2" holes twice just to see if the tap would start the same. It did every time. On my machine the quill is not under CNC so I can still use it by hand. If I were worried about tap breakage, I would use the machine to position the tapping head then bring it down by hand. That way I would have control of the torque by use of the clutch in the tapping head.

Vince