PTFE instead of Brass?

[Heffalump]

Hiya chaps,

I'm about to start making a bearing for a small oscillator, (thread to come) and the bearing calls for Brass or Bronze, neither of which I have in the right size at the moment. What I DO have, is some PTFE bar of the right size. My gut tells me that PTFE is good for a bearing, am I right? What is the SFM of PTFE? I'm guessing I'll need to crank the lathe up to a good speed!

Thanks

 

[dave-in-england]

.

Depends on the maximum revs of your lathe, and the diameter of the piece you want to cut.

but 750 feet per minute surface speed, 0.005" / rev.
0.020 depth of cut, razor sharp edge tool steel with minimum tip radius and deep rake angle.

with some coolant will give a smooth finish.

.

 

[BaronJ]

Hi Heffalump,

One of the problems with PTFE (teflon) is that it cold flows. So whilst it is good for a bearing it needs mechanical support. You will find that your hole for the bearing will grow in size over time. You would be better off using a piece of brass or bronze. I've used brass pins from old 15 amp plugs before now.

 

[Tin Falcon]

Decisions decisions.
Well my lad sometimes the best material is what you have in hand.
That said I have to agree that virgin teflon while having excellent low friction has little compression strength it makes great seals for certain applications. but there are much better materials and even much better plastics for bearing . .
Dupont vessel makes excellent bearings but is costs a kings ransom Tens of dollars per inch.
I came across this guide sheet it may help you choose.

http://www.advindustrial.com/pdf/PT%20Plane%20Brgs%20Guide_.pdf

Tin

 

[BaronJ]

Decisions decisions.
Well my lad sometimes the best material is what you have in hand.
That said I have to agree that virgin teflon while having excellent low friction has little compression strength it makes great seals for certain applications. but there are much better materials and even much better plastics for bearing . .
Dupont vessel makes excellent bearings but is costs a kings ransom Tens of dollars per inch.
I cam across this guide sheet it may help you choose.

http://www.advindustrial.com/pdf/PT%20Plane%20Brgs%20Guide_.pdf

Tin

Hi Guys,
That's a good summery of the various types of plastic materials. But you would still have to research the characteristics for the particular plastic you are going to use.

 

[dave-in-england]

.

It will only be a light duty bearing, not running all day or taking you to work and back.

Why not use some Nylon 66 or Acetal round bar, it will be a lot cheaper than ptfe, and easier to machine.

White Acetal does not push away from the tool as ptfe does, it cuts in a crisp manner similar to brass, and
it is easy to turn to tight limits.

Ebay is a good place to find this.


http://www.ebay.co.uk/itm/Acetal-Pl...t=LH_DefaultDomain_3&var=&hash=item1c3a8d0e8c


.

 

[geoff p]

Wood! Dirt cheap, holds oil, hard-wearing. Many North Sea fishing-boats used lignum vitae for rudder-post bearings, with the rudder-post clad in stainless-steel. We used to "spray" the stainless powder within a flame (can't remember the details) onto the mild-steel shaft then grind it to size (about 4 - 6 inches diameter)

When stuck for a stern-tube bearing for my model boat, I bunged a "bit of wood" in and drilled it through 4mm. Works very nicely, thank you.

Geoff,
Thailand

 

[BaronJ]

Wood! Dirt cheap, holds oil, hard-wearing. Many North Sea fishing-boats used lignum vitae for rudder-post bearings, with the rudder-post clad in stainless-steel. We used to "spray" the stainless powder within a flame (can't remember the details) onto the mild-steel shaft then grind it to size (about 4 - 6 inches diameter)

When stuck for a stern-tube bearing for my model boat, I bunged a "bit of wood" in and drilled it through 4mm. Works very nicely, thank you.

Geoff,
Thailand

I agree about the hard wood. I used to have access to a wood turning lathe that used wood for the headstock bearings. Soaked in oil and dead quiet. Flat belt drive from a motor bolted to the roof joists. Unfortunately when I moved it stayed. Don't know what happened to it when the building got demolished.

 

[rleete]

I have successfully used Kynar for bushings in engines. Holds up pretty well, but the engines don't get run for long periods.

 

[BaronJ]

Hiya chaps,

I'm about to start making a bearing for a small oscillator, (thread to come) and the bearing calls for Brass or Bronze, neither of which I have in the right size at the moment. What I DO have, is some PTFE bar of the right size. My gut tells me that PTFE is good for a bearing, am I right? What is the SFM of PTFE? I'm guessing I'll need to crank the lathe up to a good speed!

Thanks

Just wondering, did you decide on the material you are going to use ?

 

[canadianhorsepower]

Just wondering, did you decide on the material you are going to use ?
__________________

with all these info, if he wasnt lost before now he isRof}Rof}

 

[BaronJ]

with all these info, if he wasnt lost before now he isRof}Rof}

Naw ! I'm sure he will figure it out...

 

[Heffalump]

Just wondering, did you decide on the material you are going to use ?

I did! See build thread here: http://www.homemodelenginemachinist.com/f31/simple-oscillator-first-project-22577/

I decided that as I had lots of PTFE lying around I would try using that, and if it doesn't work I'll use brass. Let's face it, it's not going to have a hard life!

 

[BaronJ]

I did! See build thread here: http://www.homemodelenginemachinist.com/f31/simple-oscillator-first-project-22577/

I decided that as I had lots of PTFE lying around I would try using that, and if it doesn't work I'll use brass. Let's face it, it's not going to have a hard life!

Hi,
I shall watch your thread with interest.