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Need some advise from the experts


motor-vater
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Not asking anyone to do my job just need a push in the right direction. I am not sure the best machining strategy to take on this. This is an example piece I whipped up. Real file is not for sharing but youll get the idea. Its Delrin, and hollowed in the middle. My first instinct is to do the bottom first because fixture it from the top after the top has been machined might be somewhat more difficult. but I am worried about holding it in a vise after removing the material in the center. to tight and snap to loose and parts flying. Maybe a plug? eitherway I know the combined years of experience on here might give me some insight on how the big boys do it. As always thank you

fixturing example.jpg

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11 minutes ago, BrianP. said:

Fixture all the way. Op 1 vise. Drill holes in the middle skim top. Op 2 down on fixture hold with screws through holes. Drill corner holes, mill outside contour steps and posts. Add screws through posts cut center out . Done 2 ops.

I like 2 ops but not quiet following you. Also the corner holes are counter bored for a recessed allen head bolt from the bottom. And can you really bolt delrin down with enough force to hold it and not distort it?

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Capture.PNG.6b36463aa498a314cc9c4f9c1a130b91.PNG

You would end up something like this. And yes you can bolt it down tight enough. If you have c'bores on the back you can make islands on your fixture to locate the part or add 2 dowel pin holes in the center area to locate. Just have an M0 to add center screws before cutting it free. Very light in the vise. I have used an inch pound torque wrench to do delrin parts. Be surprised how light you can clamp when you are just facing and drilling holes.

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1 minute ago, duckdogers said:

I totally agree with fixturing if more than 1 part

The part dicates the process not me and that thin of Delrin would have to start of real thick if clamping in a vice. By tow clamping and then working from there a person can make the best part possible. Could get real crazy and super glue down and skin it and then work from there.

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We do parts similar to this from uhmw. OP1 we machine from your view shown complete from solid (holding by .100 ) leaving the window solid from the minimal thickness down, OP2 flip into step soft jaws (using inch torque), finish overall height then add 2 clamps from jaw area and finish window thru.  minimal distortion. less than .002 free state over 4" here.  HTH and GL

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23 minutes ago, CEMENTHEAD said:

We do parts similar to this from uhmw. OP1 we machine from your view shown complete from solid (holding by .100 ) leaving the window solid from the minimal thickness down, OP2 flip into step soft jaws (using inch torque), finish overall height then add 2 clamps from jaw area and finish window thru.  minimal distortion. less than .002 free state over 4" here.  HTH and GL

That will work also. Just using your vise jaws as a fixture by adding clamps. I just like all my force to be downwards. If your doing the job ok you won't over tighten it. Give it to an operator all bets are off. 6 of one half a dozen of another. Give this job to 6 people and you will get six different ways of doing it.  None of them wrong if the parts come out right. :D

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In my experience with this material it is all about "which" Delrin you get for material. If they buy the cheap stuff it will be tough regardless of the strategy. Try to encourage whoever is buying the material to get the more expensive variety from a reputable supplier.....hammer and a chisel will do it fine if you get the good stuff........if you get my drift.

I like the use the window to tool idea, used it many times, and you can use it to do both sides with a couple of dowel pins (with say 4 bolts to hold it down....gently....or maybe a plate to spread the load). Part off at least the majority on second side. You can use the part holes in the corner to stop the finished part moving at part off.

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awesome ideas here folks thanks. Yes I have to do 500 of them so a fixture is not out of the question. I was  almost thinking about the new mitee bite expansion pins for the job. That bottom part of the plate is only .100 thick when finished(not alot to hold in a vise. My original thought was do all the bottom work, drilling, counter boring and outside contour in the vise first, then flip it onto the expansion pins sized for the counter bore tighten um up and run the top ops. But now I am having my doubts. Alot of good suggestions here and the mandrels might apply to much pressure and crack the part. Bolting it down sounds good but having to move bolts in the middle of an op seems like a PITA and our operators are real princesses... decisions, decisions.

31850_catalog-Graphics_Exp3.jpg

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Double back tape

run it complete,leave .005 so not to hit the tape

if its small nest more than one

 

14 hours ago, nickbe10 said:

In my experience with this material it is all about "which" Delrin you get for material. If they buy the cheap stuff it will be tough regardless of the strategy

very true

DELRIN Brand has a porosity line in it

unless its specked in use a acetal

Doug

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I would run a larger block of material, and face the top nice and flat, and contour an accurate profile with a Rough, Semi-Finish, and Finish Cut (with Cutter Comp). I would try really hard to hold the overall length and width to +-.0005.

In Mastercam, I would use Transform > Rectangular (toolpath) to make multiple copies of the same part. Depending on length and width of the material, you may be able to get just "1 row", but do 4-6 parts, or even "multiple rows", where you are getting 18, 20, 24, or even 30 parts at a time.

I would machine all of the "internal" pocket features, and machine around the "circular bosses", but I would not "profile" the outside of the part, lower than the "top of the flange" on Side 1.

When you "flip the part over" for side 2, I would set the Work Offset to the "center of the block" and "top of the parallels", which are features I "cut" in Side 1.

For finishing on side 2, I would profile those "bosses", and face the tops of all the part surfaces.

To finish the part, I would profile (maybe Ramp), leaving a .01-.02 "web" of material holding the profile of the part, I would then take a smaller cutter, and make "Tab Cuts", which would leave just a few "Tabs" that are holding the part in place, with all the other features being finished.

When OP2 is finished, you simply use a hobby (X-acto knife) to trim the parts out.

The main benefit you get with this, is you don't you to build a fixture, and you don't have to spend any time transferring parts from OP1 to OP2.

One of the things I dislike most is making Fixtures, when you don't need to.

  • Use the Material itself, as the "fixture". In Aerospace, we call it "Window Framing". Use the "material" itself as the "fixture". The only time this doesn't work well, is with Cast or Forged parts, or "large" parts, where the extra material is expensive.
  • For smaller Delrin parts, the amount of material you are throwing away is "dollars". Sounds like money well spent, in my opinion.
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I have done parts in delrin like this in past, mill complete in the view your are showing. Buzz around them with a saw leaving a chunk of material in the inside corners. Them snap them off and sand on 320. If they are flat in backside. I have done parts in layers in a strip then transform them in the z. Just have an M0 for operator to pluck them out.

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you guys are gold! to bad the production coordinator all ready ordered the material a month ago and put this off tell now! It has now become a hot job! FML parts is a 2x2 square material is 2.25. to complicate it more I have to engrave part numbers in the bottom of the flange! Is it always like this when you take a job or did I just really win the lottery? Hes telling me we dont even have time to build a fixture he wants me to soft jaw it and let it ride....... I feel a reckoning coming!!!! I cant work like this, I really like to do things the right way even if it takes more time "the bigger picture"! Im suppost to program and get this running tonight and to top it off my lathe operator called in so I am also suppose to keep 5 lathes running with no operator.... Hahaha this is going to make Monday something to look forward too... hahaha Im just gonna machine the top in a vise and figure out how to hold it on the flip..... I love working with a gun to my head

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12 hours ago, Colin Gilchrist said:

I would run a larger block of material, and face the top nice and flat, and contour an accurate profile with a Rough, Semi-Finish, and Finish Cut (with Cutter Comp). I would try really hard to hold the overall length and width to +-.0005.

In Mastercam, I would use Transform > Rectangular (toolpath) to make multiple copies of the same part. Depending on length and width of the material, you may be able to get just "1 row", but do 4-6 parts, or even "multiple rows", where you are getting 18, 20, 24, or even 30 parts at a time.

I would machine all of the "internal" pocket features, and machine around the "circular bosses", but I would not "profile" the outside of the part, lower than the "top of the flange" on Side 1.

When you "flip the part over" for side 2, I would set the Work Offset to the "center of the block" and "top of the parallels", which are features I "cut" in Side 1.

For finishing on side 2, I would profile those "bosses", and face the tops of all the part surfaces.

To finish the part, I would profile (maybe Ramp), leaving a .01-.02 "web" of material holding the profile of the part, I would then take a smaller cutter, and make "Tab Cuts", which would leave just a few "Tabs" that are holding the part in place, with all the other features being finished.

When OP2 is finished, you simply use a hobby (X-acto knife) to trim the parts out.

The main benefit you get with this, is you don't you to build a fixture, and you don't have to spend any time transferring parts from OP1 to OP2.

One of the things I dislike most is making Fixtures, when you don't need to.

  • Use the Material itself, as the "fixture". In Aerospace, we call it "Window Framing". Use the "material" itself as the "fixture". The only time this doesn't work well, is with Cast or Forged parts, or "large" parts, where the extra material is expensive.
  • For smaller Delrin parts, the amount of material you are throwing away is "dollars". Sounds like money well spent, in my opinion.

Colin as always I'm intreged by your thought process. Although I am screwed on this project I still want a full understanding of the process for future jobs. Are you saying for example 2x2 part, use a 5x10 sheet and cut multiple parts out of it? If so toe clamp it to my table, or sacrificial plate? And If I am following you right you square the overall sheet so that you can re indicate it on the flip?

Next order of buisness would be the bottom ops, in this case surface, drill, counter bore, serial number, and then remove the center pocket material

Then the flip the sheet, re-toe clamp and surface to height, then cut in features, followed by exterior profile, and finally the last .100 cut of the profile with tabs? Does it sound like I'm getting it or did I just fly off the tracks?

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I did something  very similar to what Colin is describing....the material is the really the place holder for the part...now this was on an HMC but the premise is the same

 

eXuVLhL.png

 

That part is bolted on the front....what you cannnot see in that pic is the window opening in the back...the part is completely machine, the floor on the outer edges is only .038 thick....far too thin to flip the part and hold it on the outside,,,so both sides machined complete, then the final operation machines to outside leaving 3 tabs...the part is then snapped off complete...

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