# CNC Machinist: If Machining a 2 Stroke Crank?

Discussion in 'Workshop Tips and Secrets / Tools' started by Armilite, Feb 4, 2019.

1. Feb 4, 2019

### Armilite

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If you wanted to Machine a 2 Stroke Crank which is Pressed together in a Hyd Press, let's just use a Rotax 277UL Crank to make it Simple. You can Buy Rod kits with Crank Pins and Bearings fairly cheap. You can Buy the Crank Bearings. You can even still Buy some Replacement PTO Ends for, the 377/447, 503, 521/582, and 670. I haven't ever found anyone who makes the Mag Ends.

Most Crank Wheels Avg around 4.0 to 5.0" OD Max and the PTO/MAG Ends each Avg around Max 6.0" Long, so a piece of raw stock 5.0" x 6.0" with a little extra length for Clamping in a Lathe.

My question is, with a piece of raw Stock that has already been Faced off on both ends and Center Drilled, and OD turned for the Max Crank Wheel OD Spec, could a CNC lathe with a Tool Changer, finish the Crank in one setup?

1. Finish PTO OD Contour
2. Finish PTO Center Drill Hole to Size & Tap the End
3. On doing the Mag End Contour and Thread the End OD for Flywheel Nut.
4. The Bore & Ream Crank Pin Hole for whatever Stroke you're using?

A CNC Lathe something like this one, a 1994 Okuma-Howa ACT-20 with FANUC 18-T control Includes 8" chuck.

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2. Feb 4, 2019

### pictsidhe

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Give the operator a toleranced drawing. Figure $100 for every second he sucks through his teeth. 3. Feb 4, 2019 ### Armilite ### Armilite #### Well-Known Member Joined: Sep 6, 2011 Messages: 3,016 Likes Received: 236 Location: AMES, IA USA =============================================== Won't be any Toleranced Paper Drawings, will all done in 3D CAD/CAM and just uploaded to the machine, even though it could be entered into the Machine manually. I have Manual Machines, just never worked with CNC Machines. My Goal would be to just make Singles, PTO & Mag Ends and maybe the 1993-94 670 Mag ends. Already have a similar Single Crank parts in 3D, just need to tweak it to the Rotax Spec's. Skidoo & Rotax on their 1963+ Old Singles (247/250, 277, 292, 299/300, 318/320, 335/340) used mainly Strokes of 61mm, 66mm, 70mm. The Twins (377/380/377UL, 440/447UL, 503/503UL, 470/462UL, 521/532UL, 580/582/583/582UL, 617/618UL, 670) used mainly 61mm, 64mm, 68mm, 70mm Strokes. Some Twin Cranks are the same like (377/380/377UL, 440/447UL) and (521/532UL, 580/582/583/582UL). Some Single Cranks are the same like 66mm (247/250, 292, 299/300) and 70mm (318/320, 335/340). The newer (61mm)250 & (66mm) 277 are different in that they used a Tapered 30mm 1:10 PTO. The Older Straight Shaft PTO Singles can be upgraded to the same 30mm 1:10 PTO to use newer Clutchs or Belt/Gear Drives. This is a Billet 335/340 Single, 70mm HD Racing Crank done by a guy 8-10 years ago. It looks like he used the bigger 670 33mm 1:7.5 PTO Taper. Since all of these Singles 247 to 340 could be Big Bored to 82mm, except the newer 250, with a New Custom Sleeve. (82mm x 61mm) 322.2cc from the Newer 250 Single. (82mm x 66mm) 348.6cc from the older 247, 277, 292, 299/300. (82mm x 70mm) 369.8cc from the older 318/320, 335/340. A Simonini Single 362cc using 9.5cr = 44hp@6500rpm. A Simonini Single 382cc using 9.5cr = 48hp@6500rpm. A Simonini Single 400cc using 9.5cr = 54hp@6500rpm. The TNT & Blizzard Singles had better Cylinder Porting and can handle Bigger Carbs. My Stock 340 TNT Single came with a 38mm Carb and I'm told can go up to 44mm. The Standard 335 Cylinder can only go up to 34mm without any Machining. The 277 is limited to around 38mm I believe. All the Old Singles 1963+ (247 to 340) used the same CASE & Cylinder Shell, except for the Newer 250(72mm x 61mm) & 277(72mm x 66mm). The Cranks do interchange. The 277 PTO Case bolts onto the Older Case. Some early 247's 1963-64 used the same (4) Bolt PTO Face as the 185UL & 277UL for Gear Drives. A good used 277 Crank Avg$125 on eBay today, a Rebuilt 277 Crank $250. A Billet Single Crank can Avg$600+.
A Rod Kit Avg $80. Standard Crank Bearings Avg$20ea.
Hybrid Crank Bearings $100ea. #### Attached Files: • ###### Ski Doo TNT & Blizzard 340 single BILLET CRANK.jpg File size: 48.1 KB Views: 6 • ###### Part1.jpg File size: 42.2 KB Views: 4 • ###### Part2.jpg File size: 39.7 KB Views: 3 • ###### Part5.jpg File size: 31.6 KB Views: 5 Last edited: Feb 4, 2019 4. Feb 4, 2019 ### Deuelly ### Deuelly #### Well-Known Member Joined: Nov 6, 2012 Messages: 90 Likes Received: 82 Location: Marshall, MN I run CNC machines almost daily and it's all airplane parts. If someone came to me with a 3-D model and asked me to make it without any tolerances I'd laugh. You want me to machine a part with 20 different dimensions dead nuts? That will be$100k! They are going to need some sort of tolerances.

gtae07, proppastie, blane.c and 2 others like this.
5. Feb 5, 2019

### pictsidhe

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You must have circular breathing perfected!

6. Feb 5, 2019

### Armilite

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=========================================================

The 3D CAD Drawing has all the Dimensions & Tolerances you would need if you have a Computer to look at the 3D Model at the CNC Machine, but most CNC Shop's don't. If you was going to enter it manually into the CNC Machine and didn't have a Compter to view it then you would need a Paper Drawing with Demensions. But Most Advanced Modern Shops have a seperate CAD Area where the part is Designed, Tested on a Computer, then the 3D Model is converted to G Code for which ever CNC Machine is going to make it and then sent over the Network to that CNC Machine to be made by the Operator. These PTO Crank Parts have on Avg (2) OD Face's to contour, (1) Hole Drilled and Reamed for Crank Pin, (1) Hole Drilled & Tapped for a Bolt, and (4) edges Radiused. I said the Part would already be Faced off (2) Operations on both ends and Center Drilled (2) operations, and Max Crank Wheel OD already done (1) Operation. The most Time consuming part of the Whole Operation is Turning the 5" OD down to the Smaller Shaft OD of a Billet Part. That's why most Companies use Forgings or Investment Castings, which get's the part close to Shape then only light Machining needs done.

Today, we have Free like Fusion 360, to very Cheap CAD/CAM for the Small Shops, and the Home Hobby Guy, to use. Many Older machines have been Upgraded to run Mach 3/4 where the PC is the Controller.
https://www.machsupport.com/

Mach 3 used on a Tormach CNC lathe. 3 min to punch in Info manually.

Turning, Facing & Threading on the Tormach CNC Lathe! Widget28 Some of the same things that need done on Mag Ends.

You have 8th graders making Small Parts on CNC Lathes & Mills, as well as many Home Hobby Shop People.

Hobby Machinist.

If you think your Time to set up a CNC Machine Manually, to make (1) Simple Part like this PTO Crank Part, even if it was 20 different Dimensions, 6 different Tools to enter one time and then Save that File as Rotax 277 PTO for future Parts to be made, is worth 100K, then you know Why America is losing in the Manufacturing World. But maybe you don't. Those Stock Crank PTO's sell Retail for $75 to$125. I'm mainly Interested in doing Single Cylinder Cranks which most of the PTO/MAG Parts are the same, just different Strokes used 61mm, 66mm, 70mm. I'm Retired, so I have the TIME, I already got a Good Retirement coming in each month from the Railroad and the Wifes extra play money from her 401K, so I really don't need the extra . There is almost 8 Billion People in the World to Sell Parts to, and you can Design & Make many different Parts if you put your Mind to it.

9. Feb 5, 2019

### blane.c

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I thought you were supposed to roll up the plans and charge $1,000 per inch 10. Feb 5, 2019 ### blane.c ### blane.c #### Well-Known MemberHBA Supporter Joined: Jun 27, 2015 Messages: 2,974 Likes Received: 507 Location: capital district NY 11. Feb 6, 2019 ### Dan Thomas ### Dan Thomas #### Well-Known Member Joined: Sep 18, 2008 Messages: 4,721 Likes Received: 1,950 12. Feb 6, 2019 ### blane.c ### blane.c #### Well-Known MemberHBA Supporter Joined: Jun 27, 2015 Messages: 2,974 Likes Received: 507 Location: capital district NY Armilite likes this. 13. Feb 7, 2019 ### Armilite ### Armilite #### Well-Known Member Joined: Sep 6, 2011 Messages: 3,016 Likes Received: 236 Location: AMES, IA USA =================================================================== For a 100+ years .001" was Industry Standard for 99.9999% of the Products made for the World, Worldwide, until one day, someone got a bright idea to to go to a Higher Standard of .0005" which was really just a ploy to cut out other Countries of the World from bidding on High Dollar USA Contracts, some of these other Countries who have been known to not have the best Tolerances on their Products at that time. But many of those other World Countries stepped up their game also with better Machines and better Trained People to compete. All CAD Drawings have the Demensional Spec's on them whether on Paper or on the Computer. Today you have CAD Programs that integrate with a CAM program, like Fushion 360 Free to Students, Home Guy, even Small Shops of I think 10 People or less, is just one of many out there. "It was a scrapper to scrape muscle off bone for knee replacement. It had no need to be that precise, but it would scrap 50 at a time with those tolerances." That's one of the reasons WHY, America is losing in the Manufacturing World today. This guy is probably one of the best Modern Age CNC Machinist in the World, says it best. He is also a great motivational Speaker. Video is Long, but worth listening too! Losing$100 Million CNC Machining Contract.

G & M Code - Titan Teaches Manual Programming on a CNC Machine.

14. Feb 7, 2019

### Armilite

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Yes, 4 Stroke Cranks are made that way. These are 2 Stroke Cranks made from the different parts I showed above then Pressed together in a Hyd Press. The PTO & MAG ends are also made from either a Billet, or Forging, then Machined. The 2 Stroke Rods are usually made from either Billet or Forgings also.

The Crank Pins come with the ROD kit ready to be Pressed in. The PTO & MAG Ends have Crank Bearings that are Pressed on, some are just Heated and Slide on. If I was going to do a High Volume of Parts I would just Buy a Polisher. But I'm thinking maybe lot's of 25. I have a 12" x 37" manual lathe I can do Polishing on.

15. Feb 7, 2019

### Armilite

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Yea, the Tormach CNC Mills & Lathes have a big following, it would be a little smaller footprint than the Industrial CNC Lathe. They are not Cheap $12,000 to$15,000 depending on what Options you want. Earlier Tormachs used Mach 3 Software, Mach 4 Software is out now, but I think they use their own Software today. I have Mach 3 Software, Lathe & Mill already, account I had planned to convert my Lathe & Mill to CNC. I have had a 12" x 37" manual lathe & Mill for 20+ Years that I bought both New, and I have never turned anything much bigger than 6" OD on the Lathe, and maybe 24" Long.

Mach3
https://www.machsupport.com/

16. Feb 7, 2019

### blane.c

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17. Feb 7, 2019

### pictsidhe

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Why not make them on the lathe?

18. Feb 8, 2019

### Armilite

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Yes, there are some High-End 3D Printer Tools coming out that do Metal Work, but nothing I could afford to get into. I really like the Tormach stuff, seems pretty easy to Program your different routines. I haven't looked at the New Mach4 yet. Till I get a new place where I can have a bigger shop, I have to look at Smaller Tools or convert what I have. I have about half the stuff collected to convert my Lathe & Mill now to CNC. CNC would save me a lot of tidius work turning a Max 5" / 127mm for the Crank Wheels down to 30mm / 1.181099" for the PTO/MAG Shafts.

19. Feb 8, 2019

### blane.c

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Southwest industries link starts the slide show advertisement with a 3D printer but in a few seconds moves on to other machines, the have very capable mills that are competitive with the Tormach. I like both company's offerings quality stuff.

20. Feb 8, 2019

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