[Piet propeller]

Hello,
I design and handcarve propellers for ultralight, vintage, homebuilt aircraft in wood. 24 years later, 300 propeller designs, 2574 propellers later my lowerback has given me notice. I explored the web for 15 months looking and slowly learning about CNC routers. I have questioned all the major cnc companie - flexicam, techno, shopbot, multicam, quintax, larken shopsabre and many more. Because a propeller is not a constant object but is always changing I compiled a list of questions related to propeller carving and how a cnc router can handle the cutting of a non linear, non constant true helical blade. I eventually was contacted by ShopSabre with the most reasonable and helpfull suggestions to solve the problem of holding a propeller, digitizing one, generating a cut file etc.However, there are problems that seem fairly difficult so I sent them a TIGER MOTH vintage aircraft propeller. The help I recieved from Mike Seegar was instantaneous and reasonable and what he could not help me with he found out and called from the USA to South Africa to have a word to word discussion.
Question: Does anybody in the CNC zone know of or have cut propellerd on a CNC router system? Any practicall advice is most welcome, as well as suggestions regarding probing difficulties. I have ordered a ShopSabre and expect to recieve the machine by the end of September. I would really like to be prepared for some-but not all-surprises as I live in Africa and any relevant knowledge on cutting propellers automatically, may well be on the moon.
Thanks in advance,Piet propeller

[ajl6549]

Well, I know a 5 axis cnc machining center could do the job quite nicely with the help of MasterCam 9 or 10. SS boat prop's are made this way. As are the molds for aluminium ones. How many axis on the ShopSabre?

[lakeside]

it's 5 axis al the way one time I did a 23 foot dia. monoblock soild cast 5 blade 2 shift running code 1300 hours late

[Piet propeller]

Hello,
1)The ShopSabre I ordered has 3 axis, which would do fine as my finances only allows $22000 to $25000. The potential problem I face is that a probe is generally only 50mm in length (2"). I have to probe, at the hub area of the propeller, vertically down for 3" to 4".. The propellers are generally 72" to 86" in length and ranges in pitch from 30" to 84" are 14" to 8" wide at the hub and 3" to 6" thick at the hub so there is a variation of hub thickness from prop to prop. Shopsabre has no real solution for going down - z axis -for up to 6". I would really appreciate any advice on probing deeper than 2" without the machine assembly colliding with the propeller hub. The blades do not present any problem as 70% of the blade has a incline of 45 degrees becoming less down to about 10degrees at the tip. The probe will do the blade but it seems like I would still have to carve the hub by hand- very painfull indeed. Any solutions?

2) The problem of holding down the raw wood block on the table is of such a nature that there does not seem to be a method of clamping the blade down. Imagine the blade as a piece of twisted wood floating in the air for 80% the distance of the blade. Only the hub area will touch the table. Any suggestions here?
Thanks,
Piet propeller
Its late so i'll scoot out now and log in again tomorrow.

[ajl6549]

By "probing" I assume you mean measuring. If so, and you use a renishaw probe, they sell extensions that'll solve your problems reach.

[NEATman]

How about this thread? http://www.cnczone.com/forums/showth...ight=propeller
This approach looks as if he kept a block on the tip to prevent vibration and allow clamping.

I had seen a link somewhere here on CNCzone where you could rout out the laminates of a propeller and then power hand plane them down. What if you used a simmilar technique, use your router to first cut the laminite pieces, bond them together, then finish machine them?

NEATman

[paulC]

Hello,
1)The ShopSabre I ordered has 3 axis, which would do fine as my finances only allows $22000 to $25000. The potential problem I face is that a probe is generally only 50mm in length (2"). I have to probe, at the hub area of the propeller, vertically down for 3" to 4".. The propellers are generally 72" to 86" in length and ranges in pitch from 30" to 84" are 14" to 8" wide at the hub and 3" to 6" thick at the hub so there is a variation of hub thickness from prop to prop. Shopsabre has no real solution for going down - z axis -for up to 6". I would really appreciate any advice on probing deeper than 2" without the machine assembly colliding with the propeller hub. The blades do not present any problem as 70% of the blade has a incline of 45 degrees becoming less down to about 10degrees at the tip. The probe will do the blade but it seems like I would still have to carve the hub by hand- very painfull indeed. Any solutions?.

Could you make some sort of collar that you fit around the hub limiting the depth to the max length of probe/cutter. If you did this from each side, a 2 inch cutter could cut 2 inch from each side leaving just a piece in the middle that would need hand finishing.

2) The problem of holding down the raw wood block on the table is of such a nature that there does not seem to be a method of clamping the blade down. Imagine the blade as a piece of twisted wood floating in the air for 80% the distance of the blade. Only the hub area will touch the table. Any suggestions here?
Thanks,
Piet propeller
Its late so i'll scoot out now and log in again tomorrow.

Think you would have to cut an inverted mold from the scan then the half finished prop could be mounted in this mold to complete the machining.

Alternatly as mentioned earlier could you make it in layers and laminate them together. I assume the finished prop would be laminated anyway.
Paul

[txcowdog]

MrBean has posted his progress on a wind turbine and has a website at http://www.homemade-wind-turbines.co.uk/ This site chronicles his second build and includes making his propellers on his cnc mill

[Piet propeller]

Hi Gentleman,
Thanks for all the advice,
The renishaw is very costly and I need to fit a probe into the spindle so I wint take that route, but thank you antway AJL6549 and thanks for the sitE NEATMAN.

To Paul C - Good lord it was so obvious-about the collar - I feel ashamed but it takes an eye for detail to think the relevant questions through. I greatly appreciate your answer. Would iy be possible to conbtact you again end September 2006? I am studying RHINO 3D Nurbs, but at age 53 it is very difficult to catch uo with the 21st centuryl

[ger21]

These were $275 I think, but appear to be out of stock possibly.

http://www.cadcamcadcam.com/index.as...TS&Category=14

[Verfur]

i am in model aircraft as a hobby and have a full machine shop that i run and use. i have done many 3d parts with multi curves. What I have found on the web was a copy router that can be built cheap (not cnc). the guy is a pro propeller maker and he use just one half of the prop for the pattern that way both sides are the same. as far as holding the prop leave extra stock on the end and clamp the end and the center down and take small bites at a time. when done saw off the ends and viola.

remeber keep it simple

I think the whole st up was less than a few thousand dollors with the instructions and all.

I will try to post the web page when I get back to work.

[Piet propeller]

Good evening Gentleman,
Once again, thanks to txcowdog for the site - its worth amillion and I downloaded all of it.
Thank you for the extentions for the probe, ger21, I e-mailed the site to Shopsabre and have urged Mike Seegar to look at it urgently.
Verfur, I design and carve my own propellers but my back is killing me so I want to go the digitizing route so that in the end I have cut files of my own designs. I have a handoperated pantograph but still the accuracies is way off i.e. 2mm over a distance of 1m. In terms of pitch angkes I try to stay within 3 tenths of a mm, so 2mm is a disaster, but thanks for the suggestion and I will take a look at that site you are going to mail me.
To the moderator of the site - you seem to have a bunch of intelligent well mannered gentleman on hand. Its worth more than gold. Thank you for the oppertunity to be able to participate in such distinguished company
Best regards
Piet propeller (From the old school...)

[HuFlungDung]

Is there no method of making models of these propellers in a cad system? Does no math exist to describe the curvature?

I'd be wondering how smooth the digitised model was going to turn out, and how much work it actually is to make that g code file from the data points collected.

[lakeside]

found this on web it might be worth reading
http://www.hydrocompinc.com/knowledg...erModeling.pdf
in one of my jobs (about 2 years) did prop work at RRNM in walpole,ma 5k-75k lbs (you don't want to drop on foot) so if can do one for water there must be something for air.

[Verfur]

Piet,

Here is the web site I mentioned www.wood-carver.com/Gemini.html. Just a thought on what you are wanting to do will still take some hand working even after machined.
And the detail would reflect the amount of time spent machinig it. From the 3D metal work I have done you can easily add hours to the run time if the machine has enough memory. The only way I can see this to workk is to make molds that way its a one time investment ver days of time in one prop.

please take this as an outside look as to the fact I do not build props for a living I just machine aerospace parts from metal.

when you get it runnig It would be great to see some pics of the parts and an aprox time involved

My interset is purley for my model addiction I mean hobby.

John

[Piet propeller]

Good evening Gentleman,

Once again thanks to everybody for good advice. The knowledge gathered here will put some universities to shame .
I have managed to draw one propeller with Rhino using the advice from a windturbine site mentioned by one of the members up above. As soon as the drawing is done I shall leave it here for you gentlemen to comment on.
I would also appreciate experienced guys that have actually operated a Shopsaber to leave me with positive and negative comment so that I can counter potential problems beforehand.So far Mike Seegar at ShopSaber has really pulled out all the stops in answering the odd question or two - still I want to hear from gentlemen on the CNC Zone, so far all the comment I have read is fair and with good intention.
Best regards,
Piet Propeller

[robtown]

There's a gentleman on the shopbot forum, and I've met him at one of the shopbot jamboree's, that manufactures propellors for stunt airplanes and racing airplanes. He's been using a shopbot for this for quite some time.

His name escapes me, but if you post an inquiry at www.talkshopbot.com somebody will help you. Or, the better route would be to contact shopbot directly.

Don't know anything about the shopsabre, was close to getting one three years ago when I got my shopbot, but ended up with a shopbot, never regretted the choice. Good machine, excellent support, good user community (unmatched in the CNC world), great company.

This gentleman is based in South Africa (don't know where), and is an expert in the ways of a shopbot. His router design is based on the shopbot design with improvements. Gerald is his name and his website is: www.mechmate.com


R

[ger21]

This gentleman is based in South Africa (don't know where), and is an expert in the ways of a shopbot. His router design is based on the shopbot design with improvements. Gerald is his name and his website is: www.mechmate.com

He's a member here as well, Gerald_D. http://www.cnczone.com/forums/member.php?u=12026

[bigz1]

This software maybe of use:-

http://www.jcpropellerdesign.com/

[StealthDumpKits]

....I'd buy a full forth axis and machine it with ball end mills like a pig on a spit. Rough out everything down to say 0.250 full then finish passes slightly full with very small step over to reduce hand sanding work. Machine reference points in the hub area on both sides first. Unclamp from the fourth axis, clamp down at the hub on the table, and set up using the references to finish the blade tips. The references would be handy if/when you lose place, or to check for warpage during and after the cuts.