Progress on CNC design

After wasting most of the day with friends, I got down to work late at night. I have been writing a program to effectively choose ballscrews, stepper motors (particularly this), and gear ratios (if they are necessary.) After doing some reading for the past few days, i've come to have a much better understanding of stepper motors, torque, pulses per second, microstepping and the relationship between these design variables. The following are good reads to get you on your way for selecting a stepper setup for your machine.

http://www.cnczone.com/forums/showpost.php?p=242497&postcount=7
http://www.geckodrive.com/faq.aspx?n=8792
http://www.kelinginc.net/SMotorstock.html
http://www.cnczone.com/forums/showthread.php?t=5780
http://www.cnczone.com/forums/showthread.php?t=5866

Here is a screenshot of the program i've been working on to optimize the design features of our CNC machine build. In this case i've used it to determine the maximum feedrate of 295 IPM, according to the Torque vs. PPS chart the stepper should be yielding around 0.3 N/M of torque in a direct drive configuration. Using gear ratios, and manipulating the microstepping ratio I may be able to increase the torque for a mid to high range feedrate. As it stands 300 IPM is a bit unncessary for the metal working we'd be doing. I'll have to go over cutting forces to see if everything falls into spec. As it stands i know the linear rail system will certainly take the required loads, so the only question is if the stepper's can maintain enough torque, and if the ballscrews can take the required axial loads. (We looked up dynamic and static loads for some example ballscrews at THK and NSK)

OMG It's HOT

So we went to Canby, and bryan, bought a saw! Not just any saw, but none other than the great CHICAGO harbor freight high quality product covered in dust and cow manure. But as bryan so eloquently put it, "It cuts pretty well."

Oh and we bought some steel with troy. Purchased some square stock for my ball bearing machine frame, and bryan bought some 3" diameter steel tubing for his stirling.

TAta time for smash brothers!

Correction + CNC progress

Forgive me, I seem to have overlooked a major thing, I won a test indicator NOT a dial indicator. There is a difference, the test indicator functions as a "finger" and can be used inside holes. The Dial indicator is very sensitive to direction of setup. A finger indicator you press on from the side. I can't believe i didn't think much of it and simply "knew" what i was looking at was what i wanted, and had all the features i was looking for.

CNC progress report:

Troy and I made substantial design decisions again. I did some calculations based upon the rail and carriage dimensions determined the usable travel on the rails we are "suspected" to get. I bought one of the rail sets with the 'buy it now' feature on ebay. This included 2 used rails, and SR20 blocks from THK. Got it for 100$. We are waiting on two more rail sets to finish the deal. I really hope we win them, because if not i'll have to redo calculations. For our z-axis i'm going for some HSR carriages to ensure they can take the forces on the head.

Using the dimensions of the rails, I calculated the theoretical range of ballscrews we needed to make the most use of the rail travel. We sent off the request for these appropriately sized ballscrews to our "supplier" more info on this later.

We started to evaluate what kind of steppers we want for our setup. It looks like the 282 oz-in steppers will yield a max driving speed of 73.82 ipm. (We had to assume that the max pulse frequency is 10000 pulses per second based upon the specification chart http://www.kelinginc.net/KL23H276-30-8BT.pdf ) To do the calculations was a bit annoying because the charts we had were based in pulses per second. Using the microstepping ratio we were able to compute the approximate RPM's at a given pulse rate. Using the generated torque's on the specification chart we can compare it to the required torque for a cut a specific feed rate.

With all these calculations I've decided to start writing a program to make the process easier to repeat, and manipulate the variables for design considerations. I'll put that up later.

Won a Tenth's Dial Indicator!

I won! I got it for about 60$ shipped. Happy day, cause they typically can be anywhere from 90 to 350$ for a tenths indicator. This one comes with a few accessories, and looks like in good condition.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWNX:IT&item=190322734575

Dial Indicators

As I've been looking for a .0001 or otherwise known as a tenths indicator i inevitably decided to do some research on the given features. Apparently you want a Jeweled indicator because it won't lose precision as badly as one without it being jeweled. You also want size 2 if you have a choice, the size of the indicator has no impact on the accuracy of the indicator.

Reference:
http://longislandindicator.com/p139.html

Fly cutter complete, Scouting materials

I love scouting for materials for making things in the future. While I was looking for the appropriate sized screws at home depot and lowes for my fly cutter,

I snapped a few shots of some interesting things. Like the really low cost ryobi 8" grinding wheel for only 64$ at home depot! I've used the 6" version at the techshop and think it is indeed worth the money. Then of course there is the fellow who parked his toyota truck in classy style (namely on the curb over, and filling two complete parking spots in the middle.) Lastly this 1000 feet of seran wrap was interesting...

Troy and I have been heavily researching, and making serious design decisions about the type of ballscrews, geometry of ballscrews, spindle dimenisions, spindle bearings, dynamic loads for various parts. Grant will do the breakout board once we decide on the stepper holding torque we want. We are feeling 280-425 oz-in. The breakout board we have been looking at is rated for the current of those motors. We just wonder if we could simply pre-upgrade them from the get-go. Basically we are following the "get it right" the first time approach and researching heavily.

Hopefully we will make some more major decisions tommorow.

CNC + finished something!

The fly cutter is just about done! I drilled and tapped the fly cutter, so there is no more metal work to be done on it. The tap set i bought from hall tool (cheap chinese one) didn't work. The threads wouldn't start, I think its because they rounded the front of the taps. *sigh. The shop mechanic had some good taps that he let me borrow. I simply wish i had money to buy American all the time. All that is left to go to the store and buy longer grub screws. The ones i had bought were 1/4" long - i don't know what i was thinking when i bought them. (Picture to come later)

Other developments: I measured and designed a new airsoft part, then i went to the techshop and laser cut a 10 of them. I got the acrylic plastic from TAP plastics. Picture of a freshly cut part is below. I think i need to fine tune it because of some warping during the cuts.

Grant, Troy and I finally decided to get started on our CNC machine. I put some bids on ebay, but i was outbid. (sadface) We'll see how that goes as we progress. Now i'm doing researching doing calculations to size our ballscrews appropriately. We have access to a free 3 HP motor so it's hard to choose ballscrews that won't be able to use the motor to it's full potential. So now Troy and I are deliberating what strength screws we want.

https://tech.thk.com/en/products/thk_cat_main_fourth.php?id=878 is a good reference for determining the force a ballscrew of a given diameter can take. You'll have to convert to pounds force since it is in Newtons, but that's easy with google.

Carbon Fiber arrived!

My order of carbon fiber (2 yards) and some epoxy/hardener arrived! I also got a vapor mask because i just know my future will be filled with dangerous chemicals and plenty of dust.

I'm going to make a carbon fiber cane for my grandpa. I also went to Lowes and Home depot to buy extruded polystyrene (pink/blue stuff). It is sold in 8'x4' sections so i had to score it in the parking lot and break it in half to fit in my 4runner. Lowes didn't have it, they only had that white foam that breaks poorly (bad for sanding to a smooth finish.) So thats why i ended up going to Home Depot.

I also stopped by TAP plastics on the way. They surprisingly had carbon fiber there 60$/yard. Along with fiberglass and some other reinforcement materials. I saw mylar reflective plastic, several casting compound. They even had Delrin! I'm going to remember that for when I build a CNC or lathe. they also had some scraps for acrylic and polycarbonates. I may have to pick some up for the laser etching machine...

Today I went to the techshop with Bryan again, he accomplished a lot. I made some progress too by finishing all the milling work required for my fly cutter. But not before i broke my 2nd Niagara End mill! Gosh I feel stupid, this time it was definitely my fault. Oh well 25$ later and a hard learned lesson. Don't climb mill. Ever. I don't know what possessed me to think it would be ok. The picture below shows how it grab my part and torqued it in the vice. The mistake chipped off two flutes.

I used a 1/2" niagara 2 flute cutter to finish things off, boy was that doing a much better job at taking material off. It "felt" better too. The finish wasn't quite as smooth as cuts by the four flute, but the difference was negligible. With this cutter I faced off both sides of the fly cutter, so all that remains is 3 drill and tap operations, and i'll have a fully functional fly cutter!

Excited, overwhelmed, and tired

Bryan and I hit up sears and the Techshop today. He reminded me of the beauty of craftsman tools - the fact that you can have them easily replaced at sears. I was particularly eying the bandsaw and drill press they both were about 150$ but were decently made. I was a little concerned with the runout on the spindle for the drillpress. It looked like 10 thousands of an inch play(just a guess.)

We got to the techshop and I spent awhile setting up my dial indicator on the gorton mill. I also cracked a part of my harbor freight magnetic stand (plastic part) that clamps the dial indicator down. This happened because i effectively "overtorqued" the part. I guess thats what u get for harbor freight. It wasn't a big deal though, it still clamped down, it just had a noticeable crack in it afterwards.

Using the V-block I had finished the other day I clamped fixed up the fly cutter tool that was recently turned on the lathe. I begun milling the center slot and ran out of time. I eyed my niagara cutter again (2nd one) and noticed concave portions on the flutes. I was a bit worried about it. After I finish this operation I'm going to have my cutters reground if i can figure out where or how to do it. I still was cutting on 660 RPM with a 1/2" bit probably hand feeding at about 1 ipm. Strangely enough the cutter still makes a beautiful finish despite the dullness in the middle of the flutes.