The Stem Solution

A small shop committed to labor-saving automation added a nine-axis turning center to machine mountain bike stems. The value of this complex machine is that it delivers a simple process. The learning curve was worth it, the owners say.

For Straitline Components in Sidney, British Columbia, the difference between downhill and cross-country mountain bike racing was the difference between milling and turning. Introducing a new bike stem for cross-country riding required this small shop and bike component maker to invest in a nine-axis multitasking turning center with two workpiece spindles and the capability for five-axis milling. Company co-owner D.J. Paulson says a major part of the investment has been the learning curve he has gone through to become proficient with the machine and apply it effectively to Straitline’s new part.
 
It was worth it, he says. While Straitline certainly could have machined the part using its existing equipment—turning it on a CNC lathe and milling it on a machining center—producing it this way would have meant making and using specialty fixtures, which would add setup time and also add to the danger of setup-related error.
 
More crucially, co-owner Dennis Paulson says, “We would also have had to make fixtures just to prototype the part.”
 
The problem in this last point is that the part’s design is still being refined, even today. It is being improved for functionality, economy and manufacturability. While the new turning center is complex, that very complexity enables the machine to deliver simple processes. Because it permits single-setup processing with no need for special fixtures, the machine makes it possible to keep improving the part’s design well into production.
 
ID Gripping
 
The machining operations on the second spindle were the area of difficulty, D.J. says. The stem is not just a hardware connector, but also part of the appearance of the bike, and a rider is likely to choose a stem largely for its aesthetic appeal. Straitline’s process involved machining the part’s finished OD surface in the first spindle. Subsequently clamping the OD in the second spindle might distort the part and would almost certainly mar the attractive surface.
 
But clamping from the inside did not prove rigid enough, D.J. says. One problem was the part’s slight conical ID taper, which required chuck fingers to have the same conical profile. Another was the tendency of the chuck fingers to deflect. This led him to create preloaded fingers that would deflect into alignment with the inner surface of the part. Even with these steps, the part kept slipping. “It was baffling,” he says.
 
Worst of all, the slip often was too subtle to produce a clear and obvious defect. Just a slight slip during machining would throw the handlebar bore and steering tube bar slightly out of perpendicularity—an error that still would have to be caught because it would affect the alignment of the handlebars.
 
The solution was discovered thousands of miles away, at the International Manufacturing Technology Show in Chicago this past September. On their final day at IMTS, the brothers were making a hurried trip through the Tooling & Workholding Pavilion when they found Carbinite Metal Coatings, a company that adds tungsten alloy coatings to workholding components to improve their grip. Soon after he returned home, D.J. sent the ID grippers to Carbinite to receive this coating. As soon as the grippers returned and he re-installed them on the chuck—aligning them with the use of a sample stem part—it became clear that the coated surface would solve the problem. D.J. tried to turn the stem on the grippers by torquing it with a long-handle wrench, only to move the part, chuck and spindle all at once.
 
The brothers found another stem machining process improvement at IMTS as well. A boring tool from Criterion Machine Works that can be held in a collet chuck in the milling spindle is precisely the right size for the bore machined in the second spindle. Implementing this tool saved cycle time and improved accuracy by allowing the shop to get away from helical milling for this bore.

Tungsten Alloy Manufacturer & Supplier: Chinatungsten Online - http://www.tungsten-alloy.com
Tel.: 86 592 5129696; Fax: 86 592 5129797
Email: sales@chinatungsten.com
Tungsten News & Tungsten Prices, 3G Version: http://3g.chinatungsten.com
Tungsten News & Tungsten Prices, WML Version: http://m.chinatungsten.com

• < Prev
• Next >