Rotary table calculations

Image from: http://upload.wikimedia.org/wikipedia/commons/archive/2/2c/20080518200048!Terms_involute_gear_engagement.PNG

Rotary Table

For the rotary table we will be making a gear cutter, worm, and worm wheel. I just "figured out" an equation for calculating TPI, and worm gear teeth. Starting with S=r(theta) I derived:

60/TPI = r(2*pi)

Where 60 is the gear ratio of the worm gear to the worm wheel. Referenced below (in the previous post) is what lets you calculate the resolution that will give you on your table. The 'r' in the equation i suspect is the diametrical pitch, or namely the diameter where the force of the gear is being transmitted, not the OD of the gear. Anyways with this equation I can adjust my TPI for the cutter, and worm gear till I find a TPI that matches what the lathe is capable of cutting. Now in my research i did find that 40' was common for this application no the 60' degrees you typically see. So I need to do some more research or simply "test" it out with an ACME cutter that i already have. (I'd prefer to take the simple route)

An example calculation yielded:
8 TPI, would yield a 1.1936 radius worm wheel.

CNC update + rotary table start

I received our first CNC package of THK linear rails, they are about 30" long were used, but in great condition. My only gripe is the wipers on some of the carriages have a tendency to "catch" on the rail a little bit. I simply hand bent it up a marginal bit and it rides smooth as butter. You can see the ground sheen off them. I put electrical tape on the ends of the rails to ensure the carriages don't slide off. Pictures of these rails will come later.

I had done some research on the spindle, and found several examples of folks using treadmill motors to power their mini-cnc's typically in the 2-3 HP range, (DC motor) with an operational range of 0-6750 RPM. I didn't know much about the controller, and Troy instantly thought that was a great idea, because the VFD we were looking at for the 3 Phase 3HP motor he has would cost 300$. Where we found a treadmill on craigslist for 20$. Hopefully we can pick it up tommorow for that price. In any event he found a DC controller for the motor for less than 100$ on ebay on a 'buy it now' auction which puts at a much more cost effective solution for the motor control system.

There was also a discussion about frame materials, cost, rigidity, ease of manufacturing, and ease of transportation. So things like extruded high grade aluminum (6061), welding steel vs. warpage, and granite composite were discussed. No conclusions were drawn up with that except that we want our solution to incorporate all the attributes listed above.

When I met Troy and Bryan at the techshop. They showed me how to do assembly's in SW. This made me tremendously happy because it's like doors are being opened up for my imagination. Since we finished the fly cutter, we are now going to move onto other bigger and better projects, (which involve the use of our previously made fly cutter tehehe.) This time it is a rotary table. So I started working on modeling the rotary table on solidworks. Here is what i've got so far:



One of the problems i'm encountering is I don't know the dimensions for a standard t-slot so i went with an arbitrary depth of 1 inch and 0.25" slots. The beauty of parametric modeling, is I can go back and fix the dimensions later, Yay! I've also been playing with screw placement, clearance issues with mounting bolts and the bolts that hold the rotary table together.

The problem is I'm trying to make use of material that I already have (0.38" thick steel stock.) Which I have plenty of so I'm going to have to carefully play with the dimensions and design internal blocks to bolt everything together since 0.38" steel is not thick enough for me to comfortably drill and tap strong bolts into it. While I could calculate the yield load and fatigue life of bolts that would fit into the stock, I simply am going to use the KISS principle and oversize the bolts, and use internal mounting blocks.

References:
http://www.technologystudent.com/gears1/worm1.htm
http://www.helicron.net/workshop/gearcutting/cutting_gears/
http://www.astronomiainumbria.org/advanced_internet_files/meccanica/easyweb.easynet.co.uk/_chrish/worms.htm
http://www.cnczone.com/forums/showthread.php?t=63992

Fly cutter test

The fly cutter was tested today! Admittedly, I still have to use these silly bolts that "bump" into each other because that is all i could find at Lowe's/Home Depot. Apparently it's not wise to make something 1/4-28 NF thread. I did see quite a bit of 10-32 NF though.



I hand ground a HSS-cobalt blank on the cheap Ryobi 6" grinder at the shop. I noticed the wheels were pretty dirty from dust/aluminum. So I located the dresser, and dressed both wheels (they were in bad condition.) From there I found a bucket of water and got to work using cnccookbook.com as a guide. The rounded edge for cutting was the hardest part. I think i took a little too much off so it likes like 10-20 thousands wide, where the guide i read said you should go for 3-6 thousands. Oh well. It worked!

Here is a v-block i used earlier, and i faced one side with the fly cutter in a jiffy, hand feeding around 4ipm at 660 rpm. (High speed i know - but there is no lower gear on that machine.)

CNC update

I have successfully purchased all the linear rails i'll need for the CNC. They all are THK brand, the Z-axis has HSR20 carriage blocks for the moment load. The x and y axis are on SR20 and SR25's. We'll use the SR25's on the X-axis to take the weight of the Y-axis. The lengths for each axis are:

x-axis = 32.25"
y-axis = 29-7/8"
z-axis = 20"

Now these linear rail length's are the total length not the travel length, because the carriages when bolted up to the table mounting plate will be taking something like 8" off the total travel. So a rough guess of our work envelope will be something like:

x-axis = 24"
y-axis = 22"
z-axis = 12"

We now are working on locating screws and purchasing screws. I also purchased http://www.hobbycnc.com/products/hobbycnc-ez-driver-board-kit/ for 64$. We are holding off on the steppers for just a bit to finalize our torque requirements. Troy has been busy on the spindle design. He sucessfully modeled it up in SW, and he is performing FEA calculations on it. While I did find him some angular contact bearings that dimensionally work, and financially work, they did not have specifications on the tolerances. Troy has been working on some equations he can apply to ensure everything falls into our safety factors.



I have been keeping a spreadsheet on expenditures... Oh man it's starting to add up. I alone have purchased 450$ worth of parts specifically for our CNC alone. Troy special ordered some 4340 for his spindle for 50$. He also needs to make a tool post grinder, take a safety milling class, and buy angular contact bearings, and a VFD (300$) all for the spindle. This is going to hurt our pockets. This is really going to start being the "test" on us, we are on a tight budget (our own pocket money no less.) Our wits, our ability to scrounge, our courage, and our vigor are all going to be necessary to get through this project. The last project that i have taken part in that is of this magnitude was the 2008 HPV project. That said back to research!

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.

Intended tools for fabrication

I keep looking for simple tools and projects to build with troy. I just stumbled across this gem:
http://www.cnccookbook.com/CCButtonVBlock.htm

A button v-block can hold a work cylindrical part securely in a variety of machines, lathe, CNC, mill. Now I have to figure out how I'm going to get access to a 45 degree gauge block. Hmm perhaps I'll just CNC one.

Had a peaceful day

I didn't do any machining today, just reading/researching and relaxing. Had a nice family dinner at baja fresh. I'm going to list some of the wonderful machining sites i have come across for reference purposes:



Suppliers:

• http://www.use-enco.com/
• http://www.harborfreight.com/
• http://www.alaskancopper.com/ (local for brass)
  

Machining Tips/information

• Squaring a block on a mill - http://jjjtrain.com/vms/mill_squaring/mill_squaring_06.html
• Tool Grinding 1 - http://www.mini-lathe.com/Mini_lathe/Tool_grinding/tool_grinding.htm
• Tool Grinding 2 - http://www.sherline.com/grinding.htm (this worked great for me!)
  
• Machining accessories - http://www.mini-lathe.com/Mini_lathe/Accessories/accessories.htm
• Making a Dovetail Cutter - http://www.cnccookbook.com/MTMillDovetail.htm
• Cutting Speeds - http://its.fvtc.edu/machshop2/Speeds/RPMcalc.htm
• Surface finish on lathe - http://www.cnccookbook.com/CCLatheSurfaceFinish.html
• Simple PIC breakout board for CNC - http://www.pminmo.com/3axisPIC/3axisPIC.htm
  
• Decimal Based Thread/Screw Tap charts - http://www.shender4.com/thread_chart.htm
  
• My thread about broken mill - http://cnczone.com/forums/showthread.php?t=85804 (my thread)
• SolidCAM tutorials - http://www.solidcam.com/getting_started_en,44790.html
  

Project Inspiration:

• http://homepage3.nifty.com/amigos/index-e.html
• http://home.scarlet.be/mini-draaien-frezen/engels/projecten.html
• http://www.cartertools.com/
• http://www.finelinehair.com/home/
  

Starting to machine

So I visited troy's house today. He has an amazing pad for building and working on stuff! I'm so glad he's working on projects with me. Once we rallied up, we went to a local scrap yard, and purchased 170 pounds of steel. Split up evenly that set out to be about 30 bucks each person, which I found amazingly low cost.

By the time we did a few errands and made it to the shop to start working it was 4:00. We were pinched on time so we got right to work, this cold-rolled steel stock we was better than the "drive axle" metal that I had attempted to machine the previous night. We are setting out to make two fly cutters including arbor. I was plagued with chatter from one of these machines (which hadn't happened to me before with my grinded HSS). I tried 3 different tools, several different compound angles, and cutting fluid, along with various cutting speeds. It was a southbend lathe at fixed gear ratios so the speed ranges were a little limited. Looking at charts for cutting speed were negligibly useful because there was no indication of speed anywhere on the machine.

So after switching to another southbend and yet again another cutting tool I found a setting that worked (no/little chatter)! The cutter was darn near perpendicular to the work piece, for whatever reason this worked best. I set to work taking about 20 thousand/25 thousand cuts. Fairly deep - time was alas limited. The workpiece got fairly hot, hot enough that i wouldn't want to touch it for more than a second or two. I stopped there to let the workpiece cool off. I was glad we were making progress, as it took so long to setup and get a setting that would reasonably cut. Meanwhile, Troy had finished regreasing/rebuilding a harbor freight grinder.

A good day.

Solid Modeling Packages...

How many packages??
At OIT I learned Autocad for drafting, and IDEAS for solid modeling, and FEA. Having to switch between two software titles was mildly annoying. I heard that this year they are switching completely to solidworks, and/or CATIA for both FEA and Solid modeling. After talking to my professor and friends, I discovered industry tends to prefer solidworks/CATIA. So i basically learned all the fundamental modeling/FEA concepts on a bug-ridden IDEAS package that I most likely will never use again.

Solidworks is awesome!
This summer I picked up the solidworks book my school will use from the bookstore, and just dove in. I'm a little past halfway through the book, and am feeling very good about solidworks. It actually has an undo function!(unlike IDEAS which Ctrl+Z can destroy your model) Great stuff! I'm even learning a software package I may use in industry!

CNC beginnings..
Anyways, I signed up for the CNC classes at the portlandtechshop this summer. They taught TurboCAD and TurboCAM to model/generate G-code for the mach3 controller on their prolight Desktop CNC. I was less than impressed with turbocad, it felt like IDEAS all over again. But at least there's undo! I made my first plastic part. Later I purchased a 1/2" 1/4" center-cutting end-mill's from hall tool. After spending with my friend Troy we were able to successfully go from a part in solidworks to a physical plastic part in real life! What a refreshing feeling. You get this immense feeling of power to imagine something and see it created before your eyes in absolute perfection (ok fine near perfection - 0.0005" tolerance)!

I absolutely love my major's.

Past Projects:
I've done too many projects to showcase them all in one sitting so I will gradually add each one with a quick little summary. Now lets begin!

Carbon Fiber RC airplane:
This project was conducted through my awesome composites class at OIT with Professor Stuart.

Dimensions
We started the project by taking an existing RC airplane and taking down dimensions which were then inputed into solidworks. Yan one of my partners did the modeling based from these dimensions for a new fuselage. We located the critical internal components from the original plane.

Plug
For a male mold we started with some leftover extruded polysterene from the Formula 1 project. It is essentially high R-value building insulation foam. Very low cost, and large in volume. With the shop's band saw I was able to quickly able to get a rough shape of the fuselage. Using some sand paper I was able to form out the shape in less than half an hour.


Layup
A class or two later we began layup of the carbon fiber and resin. I think it was 6 oz. carbon fiber we used approximately 2.5 layers on most of the body. I say 2.5 layers because the main body where it was flat was 2 layers, but with overlap over the curved portions the build up increased to 3 layers. It was simple 105/205 West System epoxy. As I recall, we had about 45 minutes of working time. I was working with primarily with Marc on this one part.

Vacuum Bagging
After layup the part was looking good, we had pretty much all the wrinkles out, but as I had never done vacuum bagging before was keen on trying it. Pretty much everyone there had no experience with vacuum bagging before. We placed the part in the 2 sheets of plastic and used sticky putty to seal the bag. There were a few issues with sealing, a bit more putty and we had that figured out. The old rickity compressor had the air out in about 15 minutes (25 psi of vacuum). We locked the bag and turned off the compressor.

Result
A week later we took the cured part out of the bag, to our dismay there was a few wrinkles caused by the bag simply crinkling up on the strange geometry of our part. Observing how much resin was pulled out of the part was a little perplexing (very little if at all - like 2 tablespoon's worth). I came to the conclusion with respect to my previous composite experiences that hand layup is better for making odd shaped composite parts. Unless the absolute best strength/weight ratio is desired in your part, vacuum forming will prove to be most troublesome with complicated parts. By that I mean you can get wrinkles, stress concentrations where you may not want them... With the bandsaw, and some drills we reinstalled the planes components, and made some test runs.

Alas none of us know how to fly RC planes correctly, and we crashed fairly quickly (first try? lol) The plane proved to be too heavy even with 2 layers of carbon fiber and a bit of foam, to sustain lift. Oh well it was fun, and with a toss or two we were able to get some short flights, and some horrific crashes. The carbon fiber fuselage took the beatings like a champ! No failures there! The propeller was the first part to fail, and that was the end of our fun :P

Summer beginnings...

About me:
Ok! So i'm going to start documenting the various projects i'm partaking on. I find myself regularly taking part or learning about new and exciting new technologies between my friends, personal interests, and my education at the Oregon Institute of Technology. I am a senior studying for a double major in mechanical/manufacturing engineering. I was previously a computer science major who has since switched and has been loving every minute of my new major.