Cutting polyurethane seals

[wonky donky]

I have decided to start a new thread rather than post on the existing Polyurethane thread & it be lost as I think this information is useful in it's own right.

For those who have haven't followed the thread questions have been asked relating to the machining of polyurethane, types & hardness's best to use as well as how to achieve a good finish.

One member said there was a trick to getting a good finish so I asked if he would share, so far no reply, Baz . Who told you about it anyway

Anyway a couple of days later a well known member telephoned me out of the blue telling me had had followed the thread & gave me details of how he works with Polyurethane.

A little background first. The member is Lawrie Amatruda, if you need your Gifford repairing, want a new pump head for your Sharp or want you Crosman 140 resealing or most other things for that matter, Lawrie is your man, he's been making seals for years. If you look at collectables on the forum you will see his name crop up quite often but he rarely posts.

So with Lawries permission I will pass on the information, grinding & cutting with sharp HSS has be covered in the link above to a point.

Lets assume you want a 5mm thick flat breech seal 10mm o/d x 3mm i/d.

It would be almost impossible to use 2 punch's to make it from sheet, the finish & concentricity would be poor, even if you tried to use a double punch (one inside the other). I know as I tried this too.

What you do is make it from rod, 90 shore & above, 95 if you can get it.

First make a sharp punch for the i/d then one for the o/d, the punch can be double ended or singles.

Then make a simple collet to take the rod.

Place the collet & rod into the lathe chuck with 5mm protruding from the collet.

Put the i/d punch in the tailstock & cut into the rod 5mm, then the same with the o/d punch.

With a holder to take a scalpel in the tool post lubricated with oil part your seal off. Simple when you know how Eh!

You get an excellent finish, I have a few offcuts received in the post today from Lawrie just to prove it together with a short sample of Polyurethane rod.

I was told to use moulded rod as opposed to extruded due to the way the molecules are arranged, it appears moulded product molecules are more random adding to stiffness & giving better memory.

Thank you Lawrie! I hope have explained it well enough.

[NickG]

just need to know how to cut a rebate now

[Snooper601]

What happens if you use carbide tools, particularly the ones designed to give a superior finish on alloy?
The CGGT inserts from Chronos.

Cheers

John

[bigtoe01]

I was told HSS, very very sharp, steep rake and a special fluid that is cooled to help keep the material cooled.

HW seals are cast, Walther seals are cast, Vortek are machined, V-Mach are ground (which i do not like)

https://www.youtube.com/watch?v=RDB_qS0Gxpg

[ELMOR FUDD]

What happens if you use carbide tools, particularly the ones designed to give a superior finish on alloy?
The CGGT inserts from Chronos.

Cheers

John

Hss or carbide inserts which are designed for cutting aluminium will do the job nicely John.
Carbide should already have a honed edge where the trick with Hss that a lot of people make is that they grind it then use the cutter straight after grinding.
What you should do with HSS is hone it with a fine stone to get it mirror finish sharp and hold only just enough out the chuck by the bare minimum to to the part done.
Once you've got the hang of it, cutting polyurethane is just like any other material and becomes second nature. Get your tools right and speed and feeds and your laughing bud.

[Benelli B76]

I have decided to start a new thread rather than post on the existing Polyurethane thread & it be lost as I think this information is useful in it's own right.

For those who have haven't followed the thread questions have been asked relating to the machining of polyurethane, types & hardness's best to use as well as how to achieve a good finish.

One member said there was a trick to getting a good finish so I asked if he would share, so far no reply, Baz . Who told you about it anyway

Anyway a couple of days later a well known member telephoned me out of the blue telling me had had followed the thread & gave me details of how he works with Polyurethane.

A little background first. The member is Lawrie Amatruda, if you need your Gifford repairing, want a new pump head for your Sharp or want you Crosman 140 resealing or most other things for that matter, Lawrie is your man, he's been making seals for years. If you look at collectables on the forum you will see his name crop up quite often but he rarely posts.

So with Lawries permission I will pass on the information, grinding & cutting with sharp HSS has be covered in the link above to a point.

Lets assume you want a 5mm thick flat breech seal 10mm o/d x 3mm i/d.

It would be almost impossible to use 2 punch's to make it from sheet, the finish & concentricity would be poor, even if you tried to use a double punch (one inside the other). I know as I tried this too.

What you do is make it from rod, 90 shore & above, 95 if you can get it.

First make a sharp punch for the i/d then one for the o/d, the punch can be double ended or singles.

Then make a simple collet to take the rod.

Place the collet & rod into the lathe chuck with 5mm protruding from the collet.

Put the i/d punch in the tailstock & cut into the rod 5mm, then the same with the o/d punch.

With a holder to take a scalpel in the tool post lubricated with oil part your seal off. Simple when you know how Eh!

You get an excellent finish, I have a few offcuts received in the post today from Lawrie just to prove it together with a short sample of Polyurethane rod.

I was told to use moulded rod as opposed to extruded due to the way the molecules are arranged, it appears moulded product molecules are more random adding to stiffness & giving better memory.

Thank you Lawrie! I hope have explained it well enough.

Sorry I did not come back on the last thread, Lawrie gave me this info quite a while ago and I did not know if he wanted it to be passed on due to the work he does. I have been making seals for a while but just for myself and friends at our club.
Baz

[Snooper601]

Hss or carbide inserts which are designed for cutting aluminium will do the job nicely John.
Carbide should already have a honed edge where the trick with Hss that a lot of people make is that they grind it then use the cutter straight after grinding.
What you should do with HSS is hone it with a fine stone to get it mirror finish sharp and hold only just enough out the chuck by the bare minimum to to the part done.
Once you've got the hang of it, cutting polyurethane is just like any other material and becomes second nature. Get your tools right and speed and feeds and your laughing bud.

Thanks Jay, I thought that might work as they look very polished and sharp in the pictures on chronos' web site.
Still got more work to do before I can use my Hardinge at home.
The 5C collet system will be ideal because there are no jaws to get in the way of the tooling.

Cheers

John

[ELMOR FUDD]

Thanks Jay, I thought that might work as they look very polished and sharp in the pictures on chronos' web site.
Still got more work to do before I can use my Hardinge at home.
The 5C collet system will be ideal because there are no jaws to get in the way of the tooling.

Cheers

John

For doing the odd seal bud that method will do you fine and see you producing to a nice quality but for production runs it gets a tad more expensive and a bit more involved method wise which I won't go in to but you'll be fine matey.

[wonky donky]

I was told HSS, very very sharp, steep rake and a special fluid that is cooled to help keep the material cooled.

HW seals are cast, Walther seals are cast, Vortek are machined, V-Mach are ground (which i do not like)

https://www.youtube.com/watch?v=RDB_qS0Gxpg

Tony have you any idea how much a multi cavity mould would cost? & have you seen the price of those profiling lathes?

I'm afraid machining is the only way to go if you don't want to spend big bucks, even then it ain't going to be cheap unless you do it yourself.

There are lots of tinkerers out there plodding away with basic machinery & little knowledge, this is for them. Also it never hurts to have more ideas, the more basic the better imo.

Lawrie, who I have never met & only spoken to a few weeks ago for the first time wanted to pass on the methods that have served him well for many years, he has kindly sent me a few images which I will try to post later.

To profile the rebate for say a HW piston head I use a slot cutter & Rota broach & then an internal grooving tool ground from HSS, It's crude, It's not pretty, I don't make many, it's basic but does the job.

[bigtoe01]

Dave

Machining is the way forward, always new it would be, i think the trick is the right material (avothane 95) the right cutting speed and tooling.

For piston seals I would machine the backs, part them off, cool them on dummy pistons then machine the front faces.

[Benelli B76]

Try negative rake tool with slight curved cutting edge and slow rpm. See how you get on.

Baz

[Shed tuner]

Lawrie lives just a few miles from me, ans is a very very knowledgeable and helpful chappie. When there's the odd obscure gun that even I am too scared to work on (which is quite unnusual), it goes straight to Lawrie ! Antique CO2s are his forte

[NickG]

Tony have you any idea how much a multi cavity mould would cost? & have you seen the price of those profiling lathes?

I'm afraid machining is the only way to go if you don't want to spend big bucks, even then it ain't going to be cheap unless you do it yourself.

There are lots of tinkerers out there plodding away with basic machinery & little knowledge, this is for them. Also it never hurts to have more ideas, the more basic the better imo.

Lawrie, who I have never met & only spoken to a few weeks ago for the first time wanted to pass on the methods that have served him well for many years, he has kindly sent me a few images which I will try to post later.

To profile the rebate for say a HW piston head I use a slot cutter & Rota broach & then an internal grooving tool ground from HSS, It's crude, It's not pretty, I don't make many, it's basic but does the job.

That's interesting, I ground a tool up, a bit like one for an internal o ring groove but wider, I plunge it in to the correct bore, then wind the cross slide out to form the groove.

[wonky donky]

LAWRIES IMAGES As promised

[Benelli B76]

LAWRIES IMAGES As promised

Helpful guy Lawrie, has formulated his system from years of repairs. Must be nice to have all that ready made tooling to hand, I have to make them up as each new seal size arrives. Still mean to get one of those large handled scalpels he uses.

Baz