Crank Balancer V-Blocks... Delrin material

[R.Brown]

Has anyone made Delrin (fancy plastic I guess) V-Block inserts for crank balancers? I use a Sunnen balancer, and am looking for something better than the white plastic ones it comes with. I heard Delrin was the material some people were making them out of with very positive results.

Thanks,
Ryan

[SchmidtMotorWorks]

If you have the time and equipment to do it....I think it would be cool to have a balancing rig that holds the crank on live centers (like you find on a lathe).

The advantage would be no more scratches ever.

Delrin is similar to nylon, you might also consider teflon or machinable wax.

I used to use a balancer that had rollers, I hatet it, sometimes no matter how hard I tried to keep it clean the journals would be scuffed.

[gn30]

for many years in our balancing shop we have used phenolic v blocks with shop roll (sandpaper)( upside down)as a bearong surface. it holds oil real well and when it wears we replace it and never wear out the v's. we balance a lot of industrial/ aerospace parts aswell as crankshafts this way. we have also built shells that hold main bearing halves for customers that only balanced a few engine families of cranks.
pat

[gn30]

bad idea. most of the time the centers are not concentric to the bearimng journals. especially after the crank has been re ground. close but not "right-on"

[Dave Koehler]

Ryan,
You can find the delrin you need at McMaster Carr and probably through any plastic firms in your area.

Later
Dave Koehler
www.koehlerinjection.com

[RRBD]

Delrin is a Trademark name for Acetal. Have you thought about Turcite or Rulon? Either one of these is used as a way material in machinery applications, so its kinda intended for the application.
Acetal, however, will work great in your application.
One thing a person should think about when using plastics is that most will swell with moisture, not a problem with this application, but just a tidbit everyone should be aware of.
Also the Porosity free version is called Acetal Copolymer....

Scott

[SchmidtMotorWorks]

bad idea. most of the time the centers are not concentric to the bearimng journals. especially after the crank has been re ground. close but not "right-on"

Not where I worked, before we ground cranks we recut the centers in a lathe in a steady rest on both ends and never offset the centers in the grinders.

[R.Brown]

Schmidt: great info, thanks!

Pat: I sent you an email with a couple of questions, interesting technique!

Dave: I read on an earlier post that you had changed your balancer to Delrin and really liked it. What kind of balancer do you have, and why did you switch to Delrin?

Scott: Great stuff, thanks! Sounds like you have some "experience" in plastics.

Calling around locally, and nobody will sell less than a 1" thick 2' x 4' sheet at $600 (Canada, eh).

I did get a great response from Interstate Plastics in Kent, Wa. They have a minimum order of $25, so I can get a 6 x 12 chunk of 1" thick Acetal... just will not see the stuff for a week or so with the border being in the way.

The salesperson from Interstate indicated that Acetal and Delrin are virtually identical, but they did not have any Delrin, and going by the price it was quite a bit higher... I believe Scott when he says Acetal going to work OK.. but what is the difference between the two?

Ryan

[Dave Koehler]

This is a CEMB machine. The original Vs were made from nylon and dragged the crank speed down too much. I had to keep them lubed (too much). Heavier cranks like diesels were impossible and I had to use the rollers for them. One other trick I did was to narrow up the surface by V-ing the material from the outside edge in. I now have approximately a 1/4 contact patch which works well.

Dave Koehler
www.koehlerinjection.com

[R.Brown]

Appreciate the info Dave,
Narrowing the outer edges is something I have done to get the v-blocks that were sent with balancer to fit some of the HP cranks with the BIG journal radius. Assuming your v-blocks are made like the ones that I have, (with two raised edges to contact the crank journal on either side of the oil hole) what is the contact area thickness that you built yours to have? This balancer comes with 3 different styles, and the each contact patch ranges from .180 to .220 wide. By Veeing them down, I have some in the .100 wide range.

thanks,
Ryan

[Dave Koehler]

Mine are only 1/2" wide to begin with. Yours sounds like the Hines style.

[RRBD]

IMO, in an application like balancing its best to eliminate as many possibilities for error as possible, hence most balancers use v-blocks instead of centers. By setting the crank in v-blocks on the journals you are using a centerless approach that ensures concentricity by using the actual bearing journals and establishing an axis that replicates the environment the crank will see during use. Even if the journals arent deadnuts concentric to each other, v-blocks will give you a "best fit" axis.

Scott

[mach9]

www.smallparts.com

I think you can get the small quantities of Delrin here. MJ

[OldSStroker]

IMO, in an application like balancing its best to eliminate as many possibilities for error as possible, hence most balancers use v-blocks instead of centers. By setting the crank in v-blocks on the journals you are using a centerless approach that ensures concentricity by using the actual bearing journals and establishing an axis that replicates the environment the crank will see during use. Even if the journals arent deadnuts concentric to each other, v-blocks will give you a "best fit" axis.

Scott

I agree Scott!

Here are a few materials you might try to replace the nylon or acetal (Delrin) which you can find online at:

http://www.mcmaster.com/

Delrin AF (13% PTFE/Teflon filled acetal) Product: 8578K414
UHMW (Ultra-High Molecular Weight Polyethylene: Product 8702K81
Premium UHMW: Product 9329K31
Oil filled UHMW: Product 84945K115
PTFE (Teflon): Product 7998K16
Glass-filler PTFE:8636K18
Roulon (modified PTFE self-lubricating): Product 5824T13 (Very high $)

[machine shop tom]

We have gone the route of making our own vee-block inserts for our Hines balancer. We have tried different materials and have found little difference ins service. The marks that end up on cranks comes from the garbage that ends up on the blocks from drilling or machining the crank.

By the time you figure out how much time you have in obtaining (gotta include your time for finding it, shipping, etc.), machining and installing your custom vee-block inserts, you may find it cheaper just to pick up the phone and order from whatever balancer manufacturer what it is you need. I have found that dinking around usually costs more than what it is worth.

I agree that vee-blocks are the best way to check a crank for run-out and for balancing. A while back we had some issues with several crank grinders (about the only thing I don't do in-house). They had problems with the intermediate mains running .002"-.004" out. (They all had the same kind of crank grinder). I determined that the grinder chucks were pulling the cranks out of line and the cranks were springing back after grinding them. But the crank guys were checking them in the machine, so they checked okay. It took a few conversations to get them to check them in vee-blocks. Once they did, howvever, they were able to see what the problem was.

tom