Re: First Engine No Plans.

[kf2qd]

By drilling with a bit of patience and then reaming in one setup you should be able to get good alignment of the 3 crankshaft journals. You don't have to horse your way through when drilling them, and then the reaming process should clean things up.

 

[kvom]

Still no lathe electric hookup. After returning from a short family trip to Florida I got some time in the shop.

First order of business was to move a 2-door metal cabinet from the old to the new garage and store all my oil containers inside.

Next I checked the milling vise for tram, having trammed the table to the spindle some time ago. My cheap DI showed .002 variation across the 6" width of the fixed jaw, so I called it good for now. I'm planning to grind the vise jaws at school and will check it again once that's done.

My next goal was to get some t-nuts for the rotary table I got with the mill. I took a pair from the clamping set and tested for fit. Width was OK but I needed to mill .08" off the bottom of each. Doing so generated a lot of chatter and blue chips! I'm not sure of what type of steel they are made of. I had a 5/8" 4-flute end mill at 350 rpm, which was only 57 SFM. Higher speed seemed to make things worse. I was take cuts of .025 with a pretty slow feed.

 

[kf2qd]

Every system has SOME error. Even the best stepper system will have some error. The problem with an open loop system - like a stepper system - is that you have no real way of knowing what your error is. A servo system, on the other hand is designed to use the error and correct for it. The error is extremely small, but you can know what your error is. A side benefit of knowing the error is that you can then know the limits of what you can expect from the machine.

Another reason for going closed loop is that you can use much more powerful and faster servo motors. It requires fancier hardware and much more software to control, but the result is that you can get things done quicker and can work with bigger machines.

Those old Bridgeport Boss CNC used some huge stepper motors and the same results (or better) can be had with much smaller servos.

The reason that NASA was willing to accept those parts made on the old Bridgeport Boss CNCs is not because they were so great and uber-precise, it was because they were then state of the art. NASA wanted their parts, and that was the best way to get them - AT THE TIME.

The advantage of stepper motors for the Home/hobby machinist is COST. For under $1000 I can get the electronics to run 4 axis. Servos are probably going to cost you more than that PER AXIS. On a small benchtop machine the speed that servos could give you is not such an advantage because you don't have as far to move so you really wouldn't notice the advantage of higher speed. If you don't have far to move you don't need to go as fast.

Motion speed on a CNC machine is another nebulous thing. I used to build 2 axis Plasma/Oxy-fuel shape cutting machines. Our had a max speed of 600 IPM. A competitor had a 1200 IPM machine. Our 600 IPM machine could complete most moves before the faster machine because we had quicker accel/decel. It took them longer to get to 600 IPM than id did us so our machine was actually quicker, theirs just had a higher top speed. CNC motion is more like a drag race than an oval race. In a drag race the quickest car wins, in an oval race the fastest car wins.

 

[pabird]

Hello group,
I’ve been soaking up as much as I can for a few months now and finally got up the courage to introduce myself. My name is Al but everyone calls me Smitty, I’m soon to be 55 yrs old. Up until about a year ago I hadn’t operated a lathe since high school. I’ve worked for the last 33yrs in a coal fired power plant in the maintenance dept so I’ve always been close to things mechanical. Anyway about a year ago I bought a 9x20 and have been busy working the bugs out of it and making improvements. My shop is “my half” of our 2 car garage. No milling machine yet just the lathe and a tool grinder and a bunch of hand tools.
I’m not on the same level as most here but I’m having a ball learning. I like the groups attitude, keeps me coming back. Smitty

 

[kf2qd]

Rubber molds are probably made out of liquid RTV. Not quite the stuff that comes in the little tubes from NAPA, but in a bigger container and liquid. Have to mix it well and get most of the air out. Pour it around teh part, let it cure and cut it with a razor blade. If you pour it in some type of box that makes teh mold a but more rigid so it is easier to use.

 

[Loose nut]

You could make the tools out of hardenable steel but the machine is more complex, they are usually a pneumatic device that hits the metal faster than you can see and has to be self adjusting to perform the way it has to work, hard to explain without see one in action. If you only have a little bit to do, you can do the same thing by hand with formers and a hammer, should be easy enough to make.

 

[IronHorse]

A company called Eastwood makes small hobbyist versions:

http://www.eastwoodco.com/jump.jsp?...RODUCT&path=1,2,1397,1406&KickerID=459&KICKER

 

[Tin Falcon]

Here is another link
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=95062
Tin

 

[kvom]

Yet once again electrician dude does not show up, so lathe is still unpowered.

I decided to actually start to make an engine part on the mill, as a shakedown run. Needed to square up and mill to size a piece of brass 1x.5x.375". Started with a piece 1.7x1.5x.4 with saw marks on 4 sides and scale on the other 2.

First problem was getting a 5/8" end mill out of the spindle. This endmill got messed up milling the t-nuts for the rotab. Bridgeport has an air-operated drawbar, but it would not undo the collet. I could tell that the end of the drawbar was not fully engaging the air motor, so took off the air unit (3 capscrews). Noted that one was loose. Loosened drawbar with a wrench and collet with a deadblow. I put the air unit back on, and tightened up the mounting screws, so drawbar did engage. I was then able to mount a .5" collet and a 4-flute endmill.

Next discovery is that when milling with the side of the endmill, it pushes the x-axis sideways yielding a poor, non-flat surface. If I limited the cuts to .02" or less then I didn't have the problem. I would have liked to lock the table, but the OEM locking screw has been replaces with a socket head capscrew whose socket is larger than any allen wrench I own. So job 1 is to replace it with an easier way to lock the x-axis.

Anyway, finally got the piece sized. Replaced the mill with a drill chuck that has a .5" shank (air now seems to work) and pilot drilled two holes. Got to test out the center-find capability of the DRO, which works well.

Then I wanted to mount the cheapo rotab I got with the mill, and discovered that none of the t-nut/threaded rods from my clamping set will work as-is to clamp it to the table. The short ones don't have enough threads and the long ones are too long. So looks like I need some threaded rod, or else I will cut two of the longest ones in half with my angle grinder.

 

[lugnut]

shred, what brand is your filer? is it like this thing I have? Mine is missing or never had the variable speed thing. I think it was a variable speed pulley of some sort. I suppose I will have to do with a single speed machine.
Mel

 

[kvom]

I found a 6" piece of 1.125" diameter 12L14 stock, and as well I ground a turning/facing HSS tool yesterday.

Today I chucked it in the 6-jaw, faced and center-drilled, hooked up the live center, and took a skim cut over 5.25" using the machine feed of .0006/rev..

With my cheap digital calipers I measured 1.117" on both ends; I then mounted my cheap DI with a magnet on the toolpost and ran it up and down. Variation is less than .001", so I'm really pleased with the accuracy of a 1942-era machine.

Tomorrow I'll take the material to school and measure with a better quality micrometer.

Now if I can just get the rest of the to-dos knocked out I might actually finish Brian's engine.

 

[leop]

the engine