Lathe shaver??

[pmercer]

Hi guys.

I'm in need of a tool, but can't find what I need. I'd describe it as a 'lathe shaver' but have clearly made that name up.. Maybe if I describe what I need it to do, someone will know of a tool??

I have a section of 225mm diameter HDPE pipe that I need to turn down just enough to get a nice surface finish on the OD. I need to turn it as a lot of the marks are too deep to sand out. I can make a jig to hold it on my lathe.

The problem is that the pipe isn't actually 225mm OD. It is slightly oval and varies from 220mm - 226mm OD. Oh, and I have 25 of these to do at 200mm long.

I was hoping that there'd be a tool out there that could maybe be spring loaded and would be able to take a pre specified cut off of an oval tube (obviously running at low speed and feed.

Any thoughts??

Thanks.

 

[crueby]

Would spinning it on the lathe, not too fast, and holding a block of wood wrapped in sandpaper against it work? Then you could go in/out with the shape while smoothing it. An alternate to the sanding block would be holding a random orbit sander against it while it spins?
Could be a neat project to make a spring-loaded cutting-tool-follower, but you might ruin several while working out the bugs.

 

[bazmak]

I did something similar to 4" od heavy wall tube for a loco smoke box
Spun lathe slow and used a 4" angle grinder with first a rough sanding disc whick spins in the opposite direction.Then smoother discs.It removed approx 4 thou easily and although it did follow the contours it also tried to take off the high spots.I ran the disc along the axis of the lathe on an angle like a coarse pitch thread.Worked well did not take long

 

[Silvergoose]

Sir, back in the 1900's I worked for a plastics company. from time to time the plastic would have a "haze" to the finish and the surface was not as smooth as the rest of the part. We could have reground the plastic and reran the part but time and money were not to be had. An old man showed my how to flame polish the surface. By passing a small propane torch over the hazed area the surface would melt slightly and flow out with very good results. It may work for you. Chuck up the tube and spin it slow, keep you eye on the surface, results should be acceptable and faster than shaving.

Good Luck

 

[pmercer]

Gents,

Thanks for all suggestions. I tried to sand the surface but some of the dings and dents are too deep. I've not tried with any sort of powered sander so I'll give that a go.
I tried with a large propane torch that I have and although it melted the plastic, it didn't fill in the dings. Maybe if I melted the surface and used some sort of roller to 'smooth' the ding out.

I'd love to make a spring loaded cutting tool follower but will persevere with your other suggestions first.

Thanks.

 

[Wizard69]

Gents,

Thanks for all suggestions. I tried to sand the surface but some of the dings and dents are too deep. I've not tried with any sort of powered sander so I'll give that a go.
I tried with a large propane torch that I have and although it melted the plastic, it didn't fill in the dings. Maybe if I melted the surface and used some sort of roller to 'smooth' the ding out.

I'd love to make a spring loaded cutting tool follower but will persevere with your other suggestions first.

Thanks.

Why not cut it with a sharp HSS tool. Spin it and machine it like any other part to round out the part.

Some plastics can be smoothed by dipping in methylene chloride. I would imagine that there are other ways to chemically smooth a part.

Somebody already mentioned the torch method.

Are these the sorts of parts that can be pressed through a die to shave them to size? Of course you would need a press but that is just another tool to buy or build.

 

[kiwi2]

If you make a mandrel which has an OD the same as the actual ID of the plastic pipe, and jam the pipe over it, the outside of the pipe should then be round and you can machine it flat. If you take fine cuts with a sharp tool, the friction between the pipe and the mandrel should be enough to hold it in place.

Regards,
Alan C.

 

[charlesfitton]

Look at the devices that are used to make wood veneer...this may be what you imagine...not sure that I see it as practical.

A sharp tool bit (as suggested) should do it, but it would have to be sharpened the correct way, and I can offer little help here.

 

[Swifty]

I'm a bit confused, your original post states that the tubes vary between 220mm and 226mm Dia. You said that you only wanted to shave a little bit off, with that variation in the tube diameters, can't you just clamp it on a mandrel and using a very sharp HSS toolbit turn the outside, it seems that size is not important.

Paul.

 

[gartof]

Google apple peeler is that what you want to do?

 

[Tin Falcon]

Why not cut it with a sharp HSS tool. Spin it and machine it like any other part to round out the part.

I was wondering this myself. sounds like a basic machining operation to me.
Unless you buy ground shaft material that is pre-finished ,variations of diameter and out of round is normal. this goes with plastic and metals. some round bar is made oversized to compensate. Sometimes you need to buy oversize to allow for finishing.
Tin

 

[pmercer]

Hi gents

Thanks for all your suggestions.

I've tried using heat to fix scratches, dings etc and have had some success. It's very slow to do and there is still a witness line where I add more material or heat it.

I don't have a press or anywhere to put one unfortunately.

The wall thickness is too thick 13.4mm to use a mandrel to force the pipe round. (With the equipment I have here)

I did initially intend to turn the OD down to round, solving a few undiscussed issues for me as well. The issue with that is what happens when the pipe is cut along its length. When you cut it, not only does the cut gap close up, but the tube wants to reduce its diameter from 225 to about 180mm. There's a huge amount of internal tension in the material. Additionally, it appears that the pipe is made out of 3 layers. It's not easy to see these, until you cut it, and then it appears as if the layers are trying to delaminate (due to internal stress).

My assumption is that as I turn the pipe on the lathe, the surface will will reduce at the top and bottom (if egg shaped). This reduces the wall thickness and the internal tension in the thicker remaining sides (left and right) will pull the tube even further out of round. I'll be honest and say that i've not tried this yet - I was hoping for some sort of tool that I could just skim the surface with.

I'll get a mandrel made up to hold the tube and give it a go. I'm still toying with making spring loaded cutting tool that runs on rollers on the surface.

I work full time, doing shift work, so my time is limited to progress or update. Thanks.

 

[pmercer]

My assumption is that as I turn the pipe on the lathe, the surface will will reduce at the top and bottom (if egg shaped). This reduces the wall thickness and the internal tension in the thicker remaining sides (left and right) will pull the tube even further out of round.

I've just re-read my reply and it's just twigged that the above assumption may be wrong. Assuming the pipe look like an egg, taller than it is wide. If I reduce thickness at top and bottom (say 1mm) the extra remaining thickness on the left and right will try and reduce diameter and pull the top and bottom together.

 

[Swifty]

Can you post a picture of the pipe ?

Paul.

 

[DJP]

If this is drain or water pipe then you may be wasting time trying to make it perfectly round. It comes in coils so it's never going to be perfectly round in cross section.

You might have luck using an internal collet that expands inside the pipe and takes the egg shape away while you refinish the outer surface.

I'm not sure why this material was chosen for the job but maybe you need to consider something more suited to machining and fine tolerances.

Just some thoughts for your consideration.

 

[pmercer]

Hi gents,

It is indeed HDPE pipe used for water or gas (normally with a coloured sheath on it). It can be bought in coils, but can also be purchased in straight lengths. I looked around and I couldn't find any other supplier of HDPE pipe at this size other than water/gas suppliers.

It must have been manufactured 'round' so I'm wondering if the way it's been stored has caused it to be squashed.

I still need to make a mandrel to hold the pipe. I'll get photos in next couple of days.

Thanks

 

[MachineTom]

An old adage that fits here is, there is. Not. Any way to polish a turd.

Step up to the counter and look at material that is designed to be machined like acetal and other uhmw material.

 

[pmercer]

HDPE is the material I wanted for various reasons. I struggled to find any other supplier.

I made some tapered inserts to act as mandrels. I then heated up the pipe @ 120c for 20 minutes and the mandrels were easy to push into the pipe at each end. Once the pipe cooled, I was able to knock out the mandrels and even after the expected contraction, the pipe was within 1mm of being round.

By drilling holes centrally in the mandrels, I was able to hold the pipe in the lathe between the chick and the tail stock. I know HDPE turns well and it didn't disappoint.

There's not enough clearance under the pipe for the carriage though so could only get about 50mm at the far end finished. I'm going to try using a fixed steady instead of the tail stock; then use a large boring bar to hopefully go down the length of the pipe. I'll try and get photos uploaded.

 

[goldstar31]

The classic way is to use an 'epicyclic ' chuck. Interesting toy to make!

However, an old 3 jaw- past really decent work) chuck or a vice should squeeze an oval to round and after 'ettling it'( an old Scots expression) it can be squeezed back to oval once more.

I did something similar on a bit of oval tubing which had been the steel leg of a pair of large branch cutters and made a holder -drilled etc- for a carbide long scraper. Just a question of squeezing in the right place- as the art mistress said to the gardener

The alternative, perhaps is a cat's head chuck. Very useful thing to make.

Hint, don't use your best 3 jaw chuck -unless you intend buying a new one anyway.

Norman