about plastic injection gear

[melvin]

dear all,

just a newbie here need help!

 

Is there any info or idea for drawing a gear for wire-cut that also can adding shinkage ratio for plastic injection.

 

thx

[Piglet Trespassers William]

Use gear c-hook

After that Xform->scale

[melvin]

thx william,

 

but, is that the teeth will shinking in different direction when injection. so that i have to select the teeth only for xform ?!

 

by the way, i have a JISB1701 gear drawing, do you know what is this standard stand for.

And, is there a brief description for the gear c-hook. i mean the pitch diameter, roll diameter, etc... since i can't found all the value for the input box.

 

best,

[Guest]

melvin,

 

usually but not always the only info you need to enter is the dia. pitch,no. of teeth ,pressure angle and whether it is external or internal.

i would just change my offsets in my wire instead of scaling.

[melvin]

offset ?? the shape will be change and it will affect the JGMA data i think.

actually i have such experience, the precision(line and shape) is ok, but it bad in JGMA data that measuring by master gear...

[Guest]

i was talking about changing your offsets to allow for the shrinkage so that when it is molded

it will be correct.but i am not a moldmaker and it won't be the last time i don't know what i'm talking about.

[edmBosto]

Melvin,

I agree with William. Once you have your gear drawn you may want to copy it to another level in case you need to see the original. Scale about the center of the gear. You can then change some small radii if needed, but it's probably not necessary.

If it's nylon and you have .012 shrinkage per inch when your original model is 1 inch dia. It would now be 1.012 for the mold cavity. Everything else will shrink in proportion when molded. I don't believe you'll do any better than that on the gear tooth size.

[Guest]

edmbosto,

 

correct me if i am wrong,but i don't see how scaling a gear will give you the correct part after it is molded.if you draw a gear and scale it,it does not match up equally along the teeth.i figured that is why changing your offsets would do it.i'm not saying this is right,just that i don't see it.

[edmBosto]

Our mold designers add shrinkage all the time in pro-e.

We get our files from them after the shrinkage is taken into effect. I've done it also in mastercam.

It works that way with all our switches and circut breakers or what ever else we make molds for.

The product designers send a pro-e part to the mold designer and then they allow for shrinkage as I mentioned. The shapes just change in proportion that is set for the scaling size.

 

It may be scaled in X,Y,Z in pro-e. All I know for certain is our company needs to do this everyday a new mold is designed.

[melvin]

sorry all,during the tw earthquake, i can't connect internet to outside country a whole day...

 

hi edmBosto,

i am interested on that is your proportional ratio always make the target precision level? let a involute curve gear be example, material is pom and the shrinkage ration i set to 1.018(as i want to make as max as), after made the mold and produced a gear, everything of the jis requirement such sharp, tooth line tooth mark, pitch etc is inspec, but it will out of spec when it measuring with the mastergear.

In this case, any idea/suggestion to solve. or the measuring way...

 

by the way, is there some ref. matter for JISB1701 standard can i found in the web ?!

 

thx

[Moldmaker74]

Gears are one of the most difficult parts to mold. The best advice I can give you is to build the cavity steel safe (orbit your electrodes in a smaller radius or use stock to leave if cutting the impression). Measure your part in the gear checker and then make your adjustments according to your results. High precision gears are rarely molded within tolerance on the first sample.

[edmBosto]

Thanks moldmaker for your great advice for Melvin.

I hope all is well for you with that 7.1 magnatude on the earthquake. Also the large aftershocks.

 

As an example if a hole in a molded plastic part has a .001 tolerance we may plan steel safe and many times I find myself needing to jig grind the hole .001 larger.

quote:

---

is your proportional ratio always make the target precision level?

---

Work to the Low or high limit of your tolerance.

Which ever is steel safe and do as Moldmaker states.

 

quote:

---

is there some ref. matter for JISB1701 standard can i found in the web ?!

---

Sorry,

I don't know of any. Maybe the machinest handbook or maybe the engineers have info on this?

[Guest]

this thread finally makes sense to me.hell,i thought he was wire edming the gear shape.

[Gilberto]

"JIS..." could be a Japanese standard like "ISO", "DIN", "ANSI",...

[melvin]

thanks moldmaker74,

i can measuring the gear in different way, but i don't really know how to make adjustment base on the result graph. now i am still concentrating to analysis the relationship between these. but, simultaneously, i would like to try to use CAD/CAM warez to help me to present/discuss the modification instruction to/with mould maker

 

(untill now, we just send the result data to mould maker, then they will help us to solve the backend problem, quote us to make a new parts or etc......so passive...i am not going to do all the thing in one place but i want to know more about the principle on the work-flow, so that we can easier to face customer/end user or etc...)

 

---here i would like to share my experiment---

i am trying in a common Spur tooth with JGMA standard level 4-5 as below:

1.this gear can meet the requirement by using mastercam c-hook and setting offset for shrinkage ratio:

 

2.this gear CAN NOT meet the requirement by using the same way as 1:

 

**the parts were measured by actually moulded parts

 

is there any idea to guide me to find out the problem...

 

Thanks all,