Learning to lathe [things]

[PhotonFanatic]

Re: Learning to lathe

Speaking of surface finishes, take a look at this:

Unfortunately, I don't know the magnification involved in these photos, but suffice it to say, I want the tooling that did the machining on the left.

Of course all you bright guys will have this figured out in a heartbeat. :laughing:

 

[Carpe Diem]

Re: Learning to lathe

Hi PhotonFanatic...

You and I are now kindred spirits!

Here are my credentials in the wide world of lathes:
http://candlepowerforums.com/vb/showpost.php?p=1504538&postcount=8


(SORRY...I just couldn`t resist!)

 

[Anglepoise]

Re: Learning to lathe

As far as a good finish is concerned, I will pass on what I know.
Now if we use a regular nice and sharp carbide or HSS tipped tool
and we make a finish cut, it will most probably come out like a very very very fine male thread. Think about it for a minute. Sharp pointy tool being traversed
along the part. A thread effect will be clearly seen under low power magnification.

Now what we need to do is blend in the hills and valleys and this is done with a tool with a rounded nose. Now I am not talking about a blunt tool, just a very sharp tool with a round tip.

Now we do another finishing traverse, same speed , same depth and same feed.
Now in theory the finish will be much much better. You can actually test this out with a parting off tool with a gentle radius. You can get an amazing finish.

Now I said above 'in theory' as for this to work, the lathe must be rigid with no play in bearings , slides etc. Otherwise the thread effect will just be swapped for a 'chatter' effect as the round nose tool has more area in contact with the part.

Upping the speed also helps to flow the hills and valleys but also can be limited by
the rigidity of setup and work piece.

On our small, inexpensive machines, we will always be somewhat compromised.

Hope this helps a bit.

 

[PhotonFanatic]

Re: Learning to lathe

Hi PhotonFanatic...

You and I are now kindred spirits!

Here are my credentials in the wide world of lathes:
http://candlepowerforums.com/vb/showpost.php?p=1504538&postcount=8


(SORRY...I just couldn`t resist!)




:lolsign: But at least I bought a lathe, rather than talking about buying one!

 

[PhotonFanatic]

Re: Learning to lathe

Anglepoise wrote:

As far as a good finish is concerned, I will pass on what I know.

Now if we use a regular nice and sharp carbide or HSS tipped tool and we make a finish cut, it will most probably come out like a very very very fine male thread. Think about it for a minute. Sharp pointy tool being traversed
along the part. A thread effect will be clearly seen under low power magnification.

Now what we need to do is blend in the hills and valleys and this is done with a tool with a rounded nose. Now I am not talking about a blunt tool, just a very sharp tool with a round tip.

Now we do another finishing traverse, same speed , same depth and same feed.

Now in theory the finish will be much much better. You can actually test this out with a parting off tool with a gentle radius. You can get an amazing finish.

[snipped]

Hope this helps a bit.

David,

Yes, your explanation is quite helpful, and that technique is one that I am aware of.

There is also the use of Wiper inserts, from the likes of Sandvik:

The wiper technology incorporates five radii to "build" the nose radius of the insert. The main cutting radius is situated at the point of the insert. Behind this radius on either side is the wiper radius itself. It is blended into the main cutting radius by using a blending radius. This reduces tool pressure by eliminating the need to use a flat as the wiper.

As the insert enters the material, its main cutting radius cuts in the same manner as a standard nose radius. The cutting action produces feed lines that are equal to the feed rate being programmed. These feed lines have peaks and valleys (also called "scallops") that can be measured using a profilometer. The trailing wiper radius removes the scallops as it passes. As a result, improved surface finishes and high feed rates are possible.

I hope to try this on my lathe at some point in time, but wipers are primarily designed for the larger, more rigid CNC machines, so I have no idea if they will work on my manual lathe. But it will be fun trying.

 

[Anglepoise]

Re: Learning to lathe

I hope to try this on my lathe at some point in time, but wipers are primarily designed for the larger, more rigid CNC machines, so I have no idea if they will work on my manual lathe.

You have hit the nail on the head. 90% of what is written on tooling tech is for production, very rigid machines. Sandvik has nice stuff but all set up for industrial use. Min order quantity on inserts is 10.Can get expensive and is not necessary for us hobbyists.

 

[PhotonFanatic]

Re: Learning to lathe

Sometimes this lathe work is much, much tougher that one might expect. Most lathes do not present any problems when it come to cutting threads, but my lathe is basically a metric lathe, and uses changegears to cut Unified National threads. Problem is that the manual doesn't give enough info to be able to determine which gears exactly to use for the standard U.S. tpi's. Nor did it provide any insight into how to operate the machine for threadcutting.

My first attempts were terrible. I just couldn't get the second pass, or the third, etc., pass of the tool to align with the first cut. I wasn't disengaging the half-nut, but I was unconnecting the gearbox mechanism that drove the leadscrew. Mistake. The real solution was to reverse the spindle! Thanks to a chapter in Machine Shop Essentials for that tidbit!

Here's a thread I'm almost proud of, except that it isn't quite 24 tpi, but real close:

 

[Anglepoise]

Re: Learning to lathe

Looks good. Very good.
Now you will have to get the change gears sorted.
Sadly " isn't quite 24 tpi, but real close:" is not going to work.

Practical Machinist website or 'Homeshopmachinist.net" will help on that.

A tip that was passed on to me you might want to put away. When you get it all sorted and you are about to commence internal threading, coat the area to be threaded with a black 'Sharpie' ink pen. Now you can see how the depth is going and when the thread has been completely formed.
Without this, it all looks shiny and is difficult to see the hills and valleys.
Good luck.

PS. Will you be offering good Crees in the future.

 

[PhotonFanatic]

Re: Learning to lathe

David,

All your tips are great--thanks for sharing them.

No, I am not about to jump on the Cree bandwagon, for a couple of reasons: 1) the Cree is a PITA if it is an unmounted LED (I would only order one on a board), and 2) Philips-Lumileds will soon have something to kick Cree's butt. Think thin film technology, think a K2 with 300 lumens at 1A by the end of 2007, lower outputs before then.

 

[yclo]

Re: Learning to lathe

Always find interesting threads in this part of the forum, here's my first attempt at knurling using a scissor type knurler on a Taig:

I didn't turn on the lathe at all, just spun the spindle by hand and tightened the knurler progressively. For some reason I couldn't get the knurler to move along the work, possibily due to the setup not being rigid enough? There's also the problem of the top knurling wheel not lining up with the bottom wheel.

The Taig can't do threads..

-YC

 

[Anglepoise]

Re: Learning to lathe

yclo.

Looks great.
Having the two knurls not exactly in line is a function of the holder and you might be able to tune things a bit with washer/spacer or a bit of machining.

The reason that you could not move the saddle was the fact that you had the full pressure on the knurls.

What you did was correct. Turned by hand and got both knurls tracking.

Once they are tracking correctly then you can back off the pressure and then traverse the saddle to lengthen the knurl. You have to loosen things a bit as the
knurls are embedded and to move them requires allot of horse power.

 

[PhotonFanatic]

Re: Learning to lathe

Another day with the lathe. Another day wasted.

Today I wanted to try for a couple of things: 1) Do my first internal threading; 2) Use my new Tripan boring tool holder that works with collets; 3) Use my four-jaw adjustable chuck and adjust it properly; and 4) Practice my drilling and boring.

The goal was to fit a Kroll switch into the end of battery tube, so that the Kroll would be flush with the outer surface when screwed in place.

First I set-up the four-jaw with the round bar, roughly 22 mm in diameter to start with. It had been used before for threading practice, so it did have a smooth section near the jaws of the chuck that I could use for indicating.

One the chuck was adjusted and everything was fine, then I brought the stock down to 18.60mm and faced the end.

Next up, drill a hole deep enough to clear the Kroll Switch, including the spring. Then I tried boring that out to my minor diameter for the 5/8-28 threads. Unfortunately, I overdid it just a tad, not enough to ruin the job, but not spec on, either.

Then I bored out a 1.75mm deep recess to accommodate the rubber boot that forms a fairly waterproof seal, if it is seated properly inside the battery tube.

Finally, a chance to use my new tool, a Tripan boring/threading bar holder that has a 27mm bore in it, into which is inserted a stainless steel sleeve that is designed to accept the W20 collets that Schaublin and my Wahli use. This is really sweet because the collet set that I have ranges from .5mm to 20mm, in half-millimeter increments. That means that regardless of the shank size of the boring tool, or threading tool, I will most likely have a collet to fit it.

Dug out the threading bar that I planned to use, put it in the right collet and tightened down everything before starting the threads.

Thanks to Anglepoise's tip on covering the area to be threaded with black ink, it was fairly easy to do the internal threading. And, of course, a Groovy provided the light to peer into the end of the battery tube.

Once the threading was done, decided to throw a few grooves into the battery tube to break up the visual monotony.

Here's what the piece looked like before inserting the Kroll switch:

And with the switch inserted:

What I didn't do that I need to work on: Bevel the area where the threads start and place a slight bevel on the bore where the rubber boot contacts the battery tube.

Sadly, all this work doesn't even come close to resulting in a usable piece.

Unless someone wants a Desktop Phallic Paperweight.

 

[PhotonFanatic]

Re: Learning to lathe

.

 

[yclo]

Re: Learning to lathe

Thanks Anglepoise, will try that when I attempt my next knurl.

PhotonFanatic - engrave something on the bottom and you have a nice stamp!

I read somewhere that you shouldn't apply too much pressure on a thin walled part, now I know why...

-YC

 

[EricMack]

Re: Learning to lathe

Another day with the lathe. Another day wasted.

Sadly, all this work doesn't even come close to resulting in a usable piece.

Unless someone wants a Desktop Phallic Paperweight.

Fred - I don't think that's wasted time at all, just the dang learning curve!

Looks great man, but hmmmm, not quite sure that shape grabs me. :green: Guess its OK if you like it...





Looks good man! :thumbsup:

 

[TranquillityBase]

Re: Learning to lathe

Show us the Tripan boring/threading bar holder...Please...:twothumbs

TB

 

[PhotonFanatic]

Re: Learning to lathe

Fred - I don't think that's wasted time at all, just the dang learning curve!

Looks great man, but hmmmm, not quite sure that shape grabs me. :green: Guess its OK if you like it...


Looks good man! :thumbsup:

But, but -- it's ribbed! That should make it more valuable in the eyes of some, no?

 

[PhotonFanatic]

Re: Learning to lathe

TB,

As you requested.

First photo shows the holder on the compound slide. In the lower left is the stainless steel sleeve with the locator pin showing. Behind that is the locking nut that will pull the collet into the toolholder and tighten the collet around the bar. The collet is to the right of the sleeve, obviously.

Next we have the pieces in place, but before the collet is closed:

And now, it is ready to go:

As I mentioned before, with a wide range of sizes available for selection from the collet set (came with the machine), I can handle boring bars with varying shank diameters:

OK, last boring picture (pun intended):

 

[wquiles]

Re: Learning to lathe

Awesome! Thanks for the pictures

Will

 

[will]

Re: Learning to lathe

What I didn't do that I need to work on: Bevel the area where the threads start and place a slight bevel on the bore where the rubber boot contacts the battery tube.

I use the same threading tool to put the bevel on the front and back of the thread. I generally put a relief, a cut a few thousanths deeper than the bottom of the thread. This eliminates the burr you sometimes get. It also makes it easier to screw the parts together.