Problem- Finishing a PVC part

[dandy7200]

Routing 1/2" pvc with 1/8" dia spiral upcuts. Feed rate 50ipm 18000rpm, taking .1" per pass. Using v-carve pro and mach3. Piece is circle with many square .12" dia pins. The problem I am having is that the 4th line of each square pin retains a little "fuzzy" from the cut. This is taking me a ton of time to clean up after milling. I am looking for a little advice on either a better machining technique or a better finishing technique to clean the part. Currently I just shave the "fuzzy" with a straight edge razor which has worked fine for the prototyping but, now as I look to make a few hundred of them the thought of doing that much clean up work has me questioning my sanity.

I have attached a picture showing part after milling.

[judleroy]

If you can tell what the part is for I can probably suggest either a different machining strategy or a different manufacturing process. Its hard for me to say what will help without knowing what kind of stresses the part will be under and what the tolerances are.
Judleroy

[dandy7200]

Part is a impeller for water pump to mix air and water. Attached is showing final application. We are making this as two parts, impeller face with pins and clutch assembly on bottom to help magnetic motor start so material must be able to be bonded. I would prefer to use delrin but the bonding issue is problem. Injection molding is not going to be cost effective for 100pc as final material cost should be under $5 ea.

[mactec54]

Hi Dandy 7200

You have to make it as one piece, I make them by the hundreds, & the volutes as well I will be molding most of the pinwheels with in the next 2 month's I have 8 different pinwheels for the different volutes that we sell, PVC does not last that long so it is not a good material choice

[dandy7200]

I've definitely considered making a jig that will allow me to flip the part and machine as one piece but it still doesn't solve the finishing issue. What material are you machining from? If your making that many pw's I guess you can tell what impeller this is. If you want to provide a quote for this part let me know.

[mactec54]

Hi Dandy 7200
Most of ours pinwheels now are molded in house, if your design works better then you should keep making them, we did not machine any on a router type machine so have never had to deal with what you are, our machines have flood coolant & do not run at 18,000 rpm which is way to fast for PVC

Yes you are making a pinwheel for the Sicce motor/pump, Have you run any that you have made, How many watts & how much air did you get

The material I use is a custom blend so is not available,But when I was machining them I used a delrin/teflon rod & still use this for any prototyping that I do now, as this is close to the blend I mold with.

[judleroy]

I believe if you have not seen this before you should check out www.hobbycast.net. All you need to do is make one part and finish it as close to perfect as you can. Your mold would be made of rubber and your part would be made at 1 every 10-20 minutes. The only finishing will be the part line. If you make 3-4 molds you can go very fast. The total cost in materials to make 200 parts should be less than 200 dollars. I have done many detailed parts this way at 100 percent success. The process can be a little tricky but saves tons of time. If you decide to try this and run into trouble I can set you on the right path. Judleroy

[dandy7200]

Mactec54, the design works well for the Sicce. We have machined the same wheel for the past few years with Eheim pumps and have not had a durability issue with PVC. We only made 30 or so this way so the finishing was not an issue though and since the pump had better starting torque the clutch was not needed. I will try backing off the RPM's and see if that helps, do you suggest a speed for this machining operation?

Judleroy, I have considered casting resin for this as well. Hobbycast told me their resins would not be durable enough and sent me to http://www.bjbenterprises.com/category.asp?category=5. When I talked to bjb they confirmed the shore d resin would be more than sufficient for the intended use but we had some concerns about the part releasing from the mold with all of the pins. Do you have experience casting a similar type part? Any tips for designing a mold that would release this? We have a two stage deep vac pump that we could use.

[mactec54]

Hi Dandy 7200

If your air numbers are more then 30SCFH/15L/M for the Sicce then may be you should be molding them I would be interested only if your numbers are or close to 36SCFH/17L/M

You are right casting them is not a good option, this part is only for machining or injection molding

[judleroy]

The mold would be designed similar to a injection mold. You should have no problem getting the part to demold but you cant just rip the part out you have to be gentle. If you try to go this route and need some help with the mold design send me a message and i'll try to walk you through it.

[dandy7200]

Mactec54, I would be happy to discuss performance in more detail as well as some benchmark standards for testing if you want to share a little about what company you work for? Feel free to shoot me a PM.

Judleroy, I am a little hesitant, probably since I am unfamiliar with the processes involved.

Not to sound ungrateful for the help and suggestions thus far but, does anyone maybe have some advice on a finishing technique or milling strategy for this PVC part?

[mactec54]

Hi dandy 7200

PM sent