Machining Plastics - How to Make a Poppet, Regulator Piston Seat, etc

[Ezana4CE]

I recently read a thread where @Vetmx made a peek valve seat or maybe it was a regulator piston seat. Anyhow, I’m interested in learning how to do this. Can those of you who have done it, explain the process or point me towards a good resource to learn how to make these parts? Please share materials and equipment used to do so. I’d appreciate it.

Caveat: I’m not a machinist, but would like to learn to make a few simple things.

 

[GeneT]

Not to over-simplify, but the best thing to do is start practicing basic turning operations - turn parts to a specific diameter, drill and bore holes to a specific diameter, and face parts - all with good surface finish. You can start practicing with just about anything, but you should certainly include the materials and tools you ultimately plan to use. Any good machining text will give you a run down of the basic process. I'd encourage you to get at least a book knowledge of each operation, after which you can hit YouTube to see it in action. The reason for the book-first approach is to help you sort the wheat from the chaff on YouTube. In the end though, you really learn through practice. You're going to have to turn some useful material into useless chips to get the hang of it.

Probably one of your first considerations (other than having, or having access to, a lathe) is going to be cutters. There are a lot of ways to approach cutters - various ready-made cutters, inserts, and grinding your own from HSS (High Speed Steel). Though it's the "long route", I recommend learning to grind your own. You can grind inserts to any arbitrary sharpness as well as being able to grind custom shapes for specific tasks. If you must use inserts, consider HSS inserts from A.R. Warner tools, or carbide inserts designed for aluminum or at least ground carbide inserts. Inserts are the subject of entire books. What you save by not learning grinding, you probably pay in dollars and time figuring out which inserts to use.

I really don't know where you're starting from - do you have a lathe? What is it? Any machining experience at all? Do you have drawings of what you'd like to make?

I have a small part I'll be making from Delrin this morning, so I'll take some pictures as I go and post them here. Perhaps that will allow you to ask specific questions, as well as giving other machinists something to comment upon. There are many ways to do just about anything in machining - having alternative ideas can be helpful. Everyone must adapt what they need to do to the tools and equipment that they have or are willing to purchase.

GsT

 

[Ezana4CE]

@GeneT I am a blank slate here. No experience whatsoever, so I’m starting from scratch.

 

[sb327]

Do you have a lathe? What is it?

Those are important to know questions for anyone trying to help you.

Dave

 

[SpiralGroove]

@GeneT I am a blank slate here. No experience whatsoever, so I’m starting from scratch.

You'll need to get a lathe that will cut material to basic tolerances.
I purchased a 12" Harbor Freight lathe for $450 back in 2014 which works for me ..... I had to fiddle with it to make it better though.

I'm no machinist either, but had some shop classes in Junior High which gave me enough insight to understand the basics.
There are many websites that can give you information to perform many tasks.

 

[Ezana4CE]

You'll need to get a lathe that will cut material to basic tolerances.
I purchased a 12" Harbor Freight lathe for $450 back in 2014 which works for me ..... I had to fiddle with it to make it better though.

I'm no machinist either, but had some shop classes in Junior High which gave me enough insight to understand the basics.
There are many website that can give you information to perform many tasks.

@SpiralGroove It seems like you got it for a decent price, although a decade ago. The price is currently $799.00 for one. I checked earlier this morning.

Do you have a lathe? What is it?

Those are important to know questions for anyone trying to help you.

Dave

@sb327 I have no knowledge, nor do I have a lathe. It was told to me that some folks are making plastic parts for airguns with hand tools. I have no idea how.

 

[ba49]

I learned the basics in shop class in high school and got lucky having a few friends who were machinists to help me learn. I would suggest checking your local trade schools and jr. colleges to see if they offer basic courses in machining. They could give you a good start.

 

[Ezana4CE]

I learned the basics in shop class in high school and got lucky having a few friends who were machinists to help me learn. I would suggest checking your local trade schools and jr. colleges to see if they offer basic courses in machining. They could give you a good start.

@ba49 Thank you for the suggestion. I looked into one earlier this morning. I'll continue to do so.

 

[Firewalker]

Look at Vevor and Grizzly for inexpensive lathes. Yes, I know, they are no South Bend but for simple, shop/hobby, they are fine.

As far as tooling for plastics, use carbide made for aluminum, they are sharp, good cup angle, they leave a fine finish.

Don't waste any time learning to grind tool steel, that's a reminent from the past. Carbide is cheap, 10 inserts for under $20. Triangular inserts give you 3 points to work. 30 cutting points per pack.

I'd spend more money on labor alone grinding tool steel.

 

[Bladesx]

machine tools+ tooling, another of the slippery slopes that drains wallets, actually for plasrics HSS works better than carbide inserts. Carbide is great for reall hard or abrasive stuff and high speed removal, but high speed on plastics is a problem unless you are dumping a lot of coolant on it due to heat build up.

 

[Ricochet]

Grizzly G4015Z - 19-3/16

G4015Z 3/4 HP Combo Lathe/Mill This lathe/mill combo is not your basic benchtop machine! The G4015Z is a precision metalworking lathe/mill. The lathe features a 16-1/2" swing, 19-3/16" between centers, and 6 speeds ranging from 185 to 1455 R.P.M. The lathe cuts inch and metric threads, features...

pittsburghsprayequip.com

One of these would be nice for an at home shop, for making simple airgun parts. I wish they'd put a collet attachment in the press spindle instead of a drill chuck tho.

 

[Firewalker]

machine tools+ tooling, another of the slippery slopes that drains wallets, actually for plasrics HSS works better than carbide inserts. Carbide is great for reall hard or abrasive stuff and high speed removal, but high speed on plastics is a problem unless you are dumping a lot of coolant on it due to heat build up.

That's not been my experience with delrin, peek or nylon. The rake angle on aluminum carbide bits leaves a mirror finish when running at high speeds. I've never used coolants on plastics.

 

[dizzums]

yes, machining is a rabbit hole within the rabbit hole, so to speak ... plastic can be tricky, it does melt ... speeds, feeds, and proper tooling as they say

 

[Firewalker]

Grizzly G4015Z - 19-3/16

G4015Z 3/4 HP Combo Lathe/Mill This lathe/mill combo is not your basic benchtop machine! The G4015Z is a precision metalworking lathe/mill. The lathe features a 16-1/2" swing, 19-3/16" between centers, and 6 speeds ranging from 185 to 1455 R.P.M. The lathe cuts inch and metric threads, features...

pittsburghsprayequip.com

One of these would be nice for an at home shop, for making simple airgun parts. I wish they'd put a collet attachment in the press spindle instead of a drill chuck tho.

I'm not sure if that's the exact one my neighbor has but the chuck dropps out when surfacing. He offered it to me but I don't like combo machines.

 

[GeneT]

No need for coolant when cutting Delrin. Plastics fall into two broad categories: thermoset (won't melt) and thermoplastics (will melt). For some thermoplastics you might want coolant, but because they melt they are usually used for injection molding and not in machined parts.

GsT

 

[GeneT]

Here's the part I'm going to make this morning. It's not an airgun part, but it's an opportunity to demonstrate some basic bits and pieces. In a nutshell I will:
1. Cut the end flat (facing)
2. Turn an appropriate length to a specific diameter (outside turning).
3. Drill a hole through the part, on center.
4. Create a counterbore (that's a larger 'hole' that doesn't go all the way through. Usuall
y used so the head of a bolt can sit flush with the top surface.
5. Cut the part off to proper thickness (parting).

GsT

 

[GeneT]

Before I start, let's look at some cutters since I mentioned that earlier.

Here are four lathe tools - "cutters". From left to right:

1. An A.R. Warner HSS insert cutter.
2. A carbide insert for aluminum. Hard to see, but notice the sharp edges.
3. A hand-ground cutter - probably what I'll use for the basic turning today.
4. A carbide insert meant for steel. It might work, because Delrin is so easy, but it's not as sharp as the aluminum cutting insert, so it would take a little more pressure to cut. When it did cut, it might dig in. Delrin is pretty forgiving, but I certainly wouldn't use it for softer plastics like UHMW.

Notice the different shapes of inserts too. There are quite a few shapes (12?, 14?) I'd have to look it up - and those are just for turning (lathe) tools. I don't know anyone who uses them all, but you pick according to what suits your work best. The 'D' (think 'Diamond') insert on the far left would probably work well for this job too. It's a relatively weak shape, so I wouldn't use it anywhere that you didn't need to in steel, but it would never have an issue with Delrin.

GsT

 

[GeneT]

After cutting a piece of (black) delrin to length, I installed it in this collet chuck. Some might say a collet chuck is the ideal way to hold this, but I'm really using it because it is what is on the lathe at the moment and I see no reason to change. If I'd had my 3-jaw or 4-jaw chuck installed on the lathe, both of those would have been fine for this job.

Generally speaking a collet chuck should work with a high degree of accuracy. Similarly a 4-jaw chuck (among other features) is capable of being adjusted very precisely. Most 3-jaw chucks are self-centering, so you don't have to adjust anything, but there's usually some loss of precision and you kind of get what you get. In this case it doesn't matter. Because I'll be turning the outside of the part to begin with, the cut part will end up being "perfectly" centered with the axis of rotation even if the outside of the raw material were off several thousandths.

A general rule of thumb is that you don't want the workpiece to stick out of the chuck more than about 3 diameters. This is a 0.25" (1/4") rod, so I wouldn't want to hang it out more than 3/4". BUT, less is always better in terms of rigidity. Since this is a thin part (0.135" thick), I'm sticking it out only far enough to be able to cut that much off, with some allowance for material that will be removed from either end as I make the piece.

 

[Ezana4CE]

Thanks @GeneT !! I can actually follow your detailed explanation in this thread.

 

[Ricochet]

I'm not sure if that's the exact one my neighbor has but the chuck dropps out when surfacing. He offered it to me but I don't like combo machines.

I'm not a big fan of combo machines either, but if i was starting from scratch, and had no equipment for running small parts, this would do a lot of things. You could probably sell that little machine pretty quick on here for your neighbor.