machining a pvc sensor holder

**jmurba** · 12th April 2008, 09:53

Hi all,
I am currently tryig to machine a sensor holder to be installed on my inhalation hose.
as the internal diameter of the pcv tube fitting I used is 63 mm I had to bore the tube internally to enhance it up to 65mm to be able to enter 3 r'22's teledyne sensors.
I used a sharp boring tool but did not obtained a nice surface state as you can see watching the picture.
how could I get a better result
my cutting parameter are , speed : 300 rpm no cutting oil no cooling liquid.
is there a better method of getting a nice surface state off a pressure pvc fitting.
regards
jean mi

Dutchy · 12th April 2008, 12:33

I'd use cooling fluid for lubrication for starters. Another tip is to (and here's where's not being a native speaker is a disadvantage so I'll try to describe) leave enough material on for the last cut. What you could do in cases like this is cut until your radius is some 1 mm off, and then take the last milimeter of in one pass instead of almost getting there and then taking another 1/10th of. I hope it helps. Oh and take your speed down. It's not like you have a factory.

**jmurba** · 12th April 2008, 13:20

Quote: (Originally Posted by Dutchy)

I'd use cooling fluid for lubrication for starters. Another tip is to (and here's where's not being a native speaker is a disadvantage so I'll try to describe) leave enough material on for the last cut. What you could do in cases like this is cut until your radius is some 1 mm off, and then take the last milimeter of in one pass instead of almost getting there and then taking another 1/10th of. I hope it helps. Oh and take your speed down. It's not like you have a factory.

Hi Thanks for advice,
as for the cooling liquid ok I could try but it is not easy, I think I need an aquarium pump and a mix of water and oil, but in which fraction ?
also I hav'ent a clue of how not to spray cooling liquid everywhere in the garage....my wife also uses the garage for painting....bye bye the pictures ...
what do you think about using a round tool ?

regards
jean mi

Skipbreather · 12th April 2008, 13:48

Another tip: How you grind your tool bit can make a BIG difference. When I built my own BOV I learned the hard way (read: lots of reject parts in scrap pile) I needed clearances in the 0.0005” range. That requires a very smooth surface. I got it by a combination of fine cuts and a (relatively) rounded radius- call it several mm- on the tip of the tool bit instead of the usual tip profile that looks like a sharp point to the casual eye. The tool bit must be very sharp, too. Plastics dull HSS bits quickly so you need to study the grinding instructions which quite possibly came with your machine. If you don’t have any handy, the article below was copied from the Sherline website. Playing w/ turning speeds also greatly affects finish. Remember, you’re thinking in feet per minute/ meters per minute past the tool bit, not just RPM. The diameter of your work piece directly affects this speed.

In the end, you’ll find that experimentation with YOUR machine with various materials- metals AND plastics- will teach you much more than you’d expect. If you are in uncharted territory- for you- ALWAYS cut a test piece first to get the basic parameters down before committing you precious I-only-have-one-of-them parts to the machine.

Ken

Dutchy · 12th April 2008, 13:50

Quote: (Originally Posted by jmurba)

Hi Thanks for advice,
as for the cooling liquid ok I could try but it is not easy, I think I need an aquarium pump and a mix of water and oil, but in which fraction ?
also I hav'ent a clue of how not to spray cooling liquid everywhere in the garage....my wife also uses the garage for painting....bye bye the pictures ...
what do you think about using a round tool ?

regards
jean mi

If you reduce speed to let's say some 100 rpm and apply cooling liquid with a paint brush only once (no need to have a continuous flow) then I think you'll have a big improvement without a big mess. The good thing about being an amateur is that you don't need to mass produce so you can do it slowly. When you do it slowly you don't need a good cooling solution. The most important advice in the previous post was the one about cutting down by a decent film instead of a tiny film.

Dutchy · 12th April 2008, 13:58

Quote: (Originally Posted by Skipbreather)

Remember, you’re thinking in feet per minute/ meters per minute past the tool bit, not just RPM. The diameter of your work piece directly affects this speed.

You are absolutely right when it comes to production work but it can more or less be forgotten when diameters are small and rotational speed is very low. I've created CNC programs that scared the sh*t out of me when trying for the first time. (Hard Metal milling into Aluminum at true production speeds)
When I do stuff manually I'm at less of 10% of production speeds to I can't be bothered to calculate

.

Tautaz · 12th April 2008, 19:07

You can use a spray bomb of oil cooler like paint bomb.

Or fill a seringe and empty it slowly on the piece if you don't have a pump.

**jmurba** · 12th April 2008, 20:02

Hi Ken,

thanks a lot for the file and advice,
as for the speed of course I know that the rpm itself means nothing in terms of cutting speed , this is the reason why I had specified the diameter.

what did you made your bov from ?

regards

jean mi

Quote: (Originally Posted by Skipbreather)

Another tip: How you grind your tool bit can make a BIG difference. When I built my own BOV I learned the hard way (read: lots of reject parts in scrap pile) I needed clearances in the 0.0005” range. That requires a very smooth surface. I got it by a combination of fine cuts and a (relatively) rounded radius- call it several mm- on the tip of the tool bit instead of the usual tip profile that looks like a sharp point to the casual eye. The tool bit must be very sharp, too. Plastics dull HSS bits quickly so you need to study the grinding instructions which quite possibly came with your machine. If you don’t have any handy, the article below was copied from the Sherline website. Playing w/ turning speeds also greatly affects finish. Remember, you’re thinking in feet per minute/ meters per minute past the tool bit, not just RPM. The diameter of your work piece directly affects this speed.

In the end, you’ll find that experimentation with YOUR machine with various materials- metals AND plastics- will teach you much more than you’d expect. If you are in uncharted territory- for you- ALWAYS cut a test piece first to get the basic parameters down before committing you precious I-only-have-one-of-them parts to the machine.

Ken

**jmurba** · 12th April 2008, 20:06

Quote: (Originally Posted by Tautaz)

You can use a spray bomb of oil cooler like paint bomb.

Or fill a seringe and empty it slowly on the piece if you don't have a pump.

do you have a brand or reference for this spray ?
is it simple V33 or something like that ?
regards

jean mi

cool_hardware52 · 12th April 2008, 22:36

Quote: (Originally Posted by Skipbreather)

I needed clearances in the 0.0005” range.

5 "10ths" is really impractical in thermoplastics. The coefficient of expansion will dictate that such tolerances cannot be practically achieved. Even measuring in that range requires controlled environs, standards, and good technique.

Quote: (Originally Posted by Skipbreather)

That requires a very smooth surface. I got it by a combination of fine cuts and a (relatively) rounded radius- call it several mm- on the tip of the tool bit instead of the usual tip profile that looks like a sharp point to the casual eye. The tool bit must be very sharp, too. Plastics dull HSS bits quickly so you need to study the grinding instructions which quite possibly came with your machine. If you don’t have any handy, the article below was copied from the Sherline website. Playing w/ turning speeds also greatly affects finish. Remember, you’re thinking in feet per minute/ meters per minute past the tool bit, not just RPM. The diameter of your work piece directly affects this speed.

Softer materials will benefit from a sharp tool. Positive rake, no honed land. That will rule out many carbide inserts. At low surface speeds, HSS tools will last reasonably long.

Soft / flexly materials can make a shallow depth of cut impractical, the material can simply deflect and "flow" around the cutter. Leaving a real "bite" for finishing is often necessary. This works against being able to "sneak up" on the finished dimension. Another good argument for some extr material for test cuts.

Larger nose radius will improve surface finish, but I will caution that in the case of less rigid work holding, or less rigid work pieces, or just plane less rigid machine tools large nose radi will tend to increase chatter. If chatter is encountered and cannot be resolved via feeds and speeds less tool contact length will often save the day.

Thermoplastics are good insulators, electrically and thermally. This fact is the single most important concern in machining thermoplastics. The work piece will heat up as the heat is not conducted away from the cutting zone

Quote: (Originally Posted by Skipbreather)

In the end, you’ll find that experimentation with YOUR machine with various materials- metals AND plastics- will teach you much more than you’d expect. If you are in uncharted territory- for you- ALWAYS cut a test piece first to get the basic parameters down before committing you precious I-only-have-one-of-them parts to the machine.
Ken

This is very good advice, buy a little extra material to experiment with.

Tobin

12th April 2008, 12:33	#2 (permalink)
Dutchy SK#007 Current Rebreather/s: Sport Kiss Other Rebreather/s: Join Date: Apr 2006 Location: Nieuwegein (The Netherlands) Posts: 699	Re: machining a pvc sensor holder I'd use cooling fluid for lubrication for starters. Another tip is to (and here's where's not being a native speaker is a disadvantage so I'll try to describe) leave enough material on for the last cut. What you could do in cases like this is cut until your radius is some 1 mm off, and then take the last milimeter of in one pass instead of almost getting there and then taking another 1/10th of. I hope it helps. Oh and take your speed down. It's not like you have a factory. __________________ = This post is environmentally friendly. It is composed of 100% recycled electrons only. = SK #007
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12th April 2008, 13:20	#3 (permalink)
jmurba wet bear Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: May 2006 Location: cannes france Posts: 672	Re: machining a pvc sensor holder Quote: (Originally Posted by Dutchy) I'd use cooling fluid for lubrication for starters. Another tip is to (and here's where's not being a native speaker is a disadvantage so I'll try to describe) leave enough material on for the last cut. What you could do in cases like this is cut until your radius is some 1 mm off, and then take the last milimeter of in one pass instead of almost getting there and then taking another 1/10th of. I hope it helps. Oh and take your speed down. It's not like you have a factory. Hi Thanks for advice, as for the cooling liquid ok I could try but it is not easy, I think I need an aquarium pump and a mix of water and oil, but in which fraction ? also I hav'ent a clue of how not to spray cooling liquid everywhere in the garage....my wife also uses the garage for painting....bye bye the pictures ... what do you think about using a round tool ? regards jean mi __________________ when will I be able to think about something else then spending hours underwater, when will I be normal ? http://web.mac.com/jmurba/Site_2/home.html http://web.mac.com/jmurba/Site_3/home.html
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12th April 2008, 13:50	#5 (permalink)
Dutchy SK#007 Current Rebreather/s: Sport Kiss Other Rebreather/s: Join Date: Apr 2006 Location: Nieuwegein (The Netherlands) Posts: 699	Re: machining a pvc sensor holder Quote: (Originally Posted by jmurba) Hi Thanks for advice, as for the cooling liquid ok I could try but it is not easy, I think I need an aquarium pump and a mix of water and oil, but in which fraction ? also I hav'ent a clue of how not to spray cooling liquid everywhere in the garage....my wife also uses the garage for painting....bye bye the pictures ... what do you think about using a round tool ? regards jean mi If you reduce speed to let's say some 100 rpm and apply cooling liquid with a paint brush only once (no need to have a continuous flow) then I think you'll have a big improvement without a big mess. The good thing about being an amateur is that you don't need to mass produce so you can do it slowly. When you do it slowly you don't need a good cooling solution. The most important advice in the previous post was the one about cutting down by a decent film instead of a tiny film. __________________ = This post is environmentally friendly. It is composed of 100% recycled electrons only. = SK #007
(Offline)

12th April 2008, 13:58	#6 (permalink)
Dutchy SK#007 Current Rebreather/s: Sport Kiss Other Rebreather/s: Join Date: Apr 2006 Location: Nieuwegein (The Netherlands) Posts: 699	Re: machining a pvc sensor holder Quote: (Originally Posted by Skipbreather) Remember, you’re thinking in feet per minute/ meters per minute past the tool bit, not just RPM. The diameter of your work piece directly affects this speed. You are absolutely right when it comes to production work but it can more or less be forgotten when diameters are small and rotational speed is very low. I've created CNC programs that scared the sh*t out of me when trying for the first time. (Hard Metal milling into Aluminum at true production speeds) When I do stuff manually I'm at less of 10% of production speeds to I can't be bothered to calculate . __________________ = This post is environmentally friendly. It is composed of 100% recycled electrons only. = SK #007
(Offline)

12th April 2008, 19:07	#7 (permalink)
Tautaz New Member Current Rebreather/s: Home Build Other Rebreather/s: Not Bought Yet Home Build Join Date: Jan 2007 Location: Colomiers France Posts: 66	Re: machining a pvc sensor holder You can use a spray bomb of oil cooler like paint bomb. Or fill a seringe and empty it slowly on the piece if you don't have a pump.
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12th April 2008, 20:02	#8 (permalink)
jmurba wet bear Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: May 2006 Location: cannes france Posts: 672	Re: machining a pvc sensor holder Hi Ken, thanks a lot for the file and advice, as for the speed of course I know that the rpm itself means nothing in terms of cutting speed , this is the reason why I had specified the diameter. what did you made your bov from ? regards jean mi Quote: (Originally Posted by Skipbreather) Another tip: How you grind your tool bit can make a BIG difference. When I built my own BOV I learned the hard way (read: lots of reject parts in scrap pile) I needed clearances in the 0.0005” range. That requires a very smooth surface. I got it by a combination of fine cuts and a (relatively) rounded radius- call it several mm- on the tip of the tool bit instead of the usual tip profile that looks like a sharp point to the casual eye. The tool bit must be very sharp, too. Plastics dull HSS bits quickly so you need to study the grinding instructions which quite possibly came with your machine. If you don’t have any handy, the article below was copied from the Sherline website. Playing w/ turning speeds also greatly affects finish. Remember, you’re thinking in feet per minute/ meters per minute past the tool bit, not just RPM. The diameter of your work piece directly affects this speed. In the end, you’ll find that experimentation with YOUR machine with various materials- metals AND plastics- will teach you much more than you’d expect. If you are in uncharted territory- for you- ALWAYS cut a test piece first to get the basic parameters down before committing you precious I-only-have-one-of-them parts to the machine. Ken __________________ when will I be able to think about something else then spending hours underwater, when will I be normal ? http://web.mac.com/jmurba/Site_2/home.html http://web.mac.com/jmurba/Site_3/home.html
(Online)

12th April 2008, 20:06	#9 (permalink)
jmurba wet bear Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: May 2006 Location: cannes france Posts: 672	Re: machining a pvc sensor holder Quote: (Originally Posted by Tautaz) You can use a spray bomb of oil cooler like paint bomb. Or fill a seringe and empty it slowly on the piece if you don't have a pump. do you have a brand or reference for this spray ? is it simple V33 or something like that ? regards jean mi __________________ when will I be able to think about something else then spending hours underwater, when will I be normal ? http://web.mac.com/jmurba/Site_2/home.html http://web.mac.com/jmurba/Site_3/home.html
(Online)

12th April 2008, 22:36	#10 (permalink)
cool_hardware52 RebreatherWorld Sponsor Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Mar 2005 Location: SoCal USA Posts: 358	Re: machining a pvc sensor holder Quote: (Originally Posted by Skipbreather) I needed clearances in the 0.0005” range. 5 "10ths" is really impractical in thermoplastics. The coefficient of expansion will dictate that such tolerances cannot be practically achieved. Even measuring in that range requires controlled environs, standards, and good technique. Quote: (Originally Posted by Skipbreather) That requires a very smooth surface. I got it by a combination of fine cuts and a (relatively) rounded radius- call it several mm- on the tip of the tool bit instead of the usual tip profile that looks like a sharp point to the casual eye. The tool bit must be very sharp, too. Plastics dull HSS bits quickly so you need to study the grinding instructions which quite possibly came with your machine. If you don’t have any handy, the article below was copied from the Sherline website. Playing w/ turning speeds also greatly affects finish. Remember, you’re thinking in feet per minute/ meters per minute past the tool bit, not just RPM. The diameter of your work piece directly affects this speed. Softer materials will benefit from a sharp tool. Positive rake, no honed land. That will rule out many carbide inserts. At low surface speeds, HSS tools will last reasonably long. Soft / flexly materials can make a shallow depth of cut impractical, the material can simply deflect and "flow" around the cutter. Leaving a real "bite" for finishing is often necessary. This works against being able to "sneak up" on the finished dimension. Another good argument for some extr material for test cuts. Larger nose radius will improve surface finish, but I will caution that in the case of less rigid work holding, or less rigid work pieces, or just plane less rigid machine tools large nose radi will tend to increase chatter. If chatter is encountered and cannot be resolved via feeds and speeds less tool contact length will often save the day. Thermoplastics are good insulators, electrically and thermally. This fact is the single most important concern in machining thermoplastics. The work piece will heat up as the heat is not conducted away from the cutting zone Quote: (Originally Posted by Skipbreather) In the end, you’ll find that experimentation with YOUR machine with various materials- metals AND plastics- will teach you much more than you’d expect. If you are in uncharted territory- for you- ALWAYS cut a test piece first to get the basic parameters down before committing you precious I-only-have-one-of-them parts to the machine. Ken This is very good advice, buy a little extra material to experiment with. Tobin __________________ www.deepseasupply.com
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