Alumilite Blank Chipping

[mgoetzke]

I'm new to turning this material. I cast the blanks so they are not totally round to start. I have been using a small round carbide tool, larger round NR carbide tool, and a skew. I have no issues with the skew but it is s_l_o_w so I pulled out the NR round carbide tool and small round carbide tool to remove the material quicker before switching to the skew. Both times with the round carbide cutters the seem to work great until the blank becomes round then I got chip-out in the middle of the blank. Luckily both times I was able to skew turn out the chipped area but wondering what is going on (I'm sure it is user error). The method I'm using with the carbide is approach straight in and sweep out the material. Maybe when I'm getting close to round don't approach perpendicular?

Thanks

 

[jrista]

There is a limit to how "fast" you can remove material with some resins. If you push the tool in too hard, I've found that pretty much any of the resins I turn will start to chip out. For alumilite as well as some other resins, you just need to take it slower...more passes removing thinner layers of material. With acrylic, I can remove almost as much as I want at a time, although I still find that if I'm too aggressive, I get ripples and other surface defects that can then be harder to get out later (usually requires more aggressive sanding, which has its own problems).

With a NR Carbide, I mostly use the same technique. I guess I don't really go "strait in". I have the tool at an angle, maybe 45 degrees on the rest, and I push in near the middle of the blank and move towards the end. Repeat a few passes of that, starting farther and farther to the other end, removing more of the bulk of the material. Once I have just a bit of material at one end, I reorient myself and the tool so I can go the other way, and just work down that bit.

I will say, when I first start, when the blank is totally square (I never cut off corners or anything like that, haven't felt the need), I start pretty light. I take off just a tiny bit of the corners at first in long passes along the entire length of the blank, until the corners are gone. Only after doing that, do I start trying to take off bulk material. I also make sure I stop with my more aggressive passes once the blank is round. Aggressive passes leave an uneven surface (at least for me), so I only just round the blank. Once its fully round, I then use more careful, slower passes to clean up the surface and work it down into my desired shape. Depending on the resin, you may get either streams of resin flowing off the blank, or the stream may immediately bundle and bunch up into a little...resin schrunchie for lack of a better term; other materials may just end up powder, or little flakes (trustone/faux stone, etc. tend to just powderize; alumilite, at least what I've turned so far, seems to be somewhere inbetween).

I like to take smaller layers of material off at this point, as I can keep the blank nice and smooth and free of those ridges and ripples and bumps you get when trying to take off say a millimeter or more of material each pass. It takes a bit longer to turn, but in the end you can get a pretty smooth, clean, reflective finish (still needs sanding and polishing, but the blank should be nice and clean and pretty darn smooth when you are done turning.)

 

[leehljp]

1. Are you using a mandrel?
2. What speed are you turning?

These are questions that usually come up way down the line in troubleshooting chip-outs after other suggestions don't match up.

WHY Mandrel question? if the mandrel is flexing, there may be more vibration in the center part. It doesn't take by 1mm flex to create that scenario.
SPEED Question: Too slow can cause a similar chip out. Many times bowl turners will turn much slower than most pen turners. Bowl turning at 12 inch diameter and 700 RPM is MUCH faster cutting speed - than the cutting speed of 3000 RPM on 3/4 inch diameter pen blanks. Too slow will cause catches and chips. It is difficult to move up to 3000 rpm when one has been doing a great job at 700 rpm for a few years.

My answer is different from John Rista's answer. He is referring to tool feed or how much of a "bite" are you taking? My answer is concerning lathe speed. Being too aggressive with the tool can cause flex, and even if no flex is there.

 

[jrista]

1. Are you using a mandrel?
2. What speed are you turning?

These are questions that usually come up way down the line in troubleshooting chip-outs after other suggestions don't match up.

WHY Mandrel question? if the mandrel is flexing, there may be more vibration in the center part. It doesn't take by 1mm flex to create that scenario.
SPEED Question: Too slow can cause a similar chip out. Many times bowl turners will turn much slower than most pen turners. Bowl turning at 12 inch diameter and 700 RPM is MUCH faster cutting speed - than the cutting speed of 3000 RPM on 3/4 inch diameter pen blanks. Too slow will cause catches and chips. It is difficult to move up to 3000 rpm when one has been doing a great job at 700 rpm for a few years.

Great point about speed... I totally agree, you need to turn fast enough, I myself turn pens around 2800-3200RPM.

I have still experienced chipout at those speeds when I'm too aggressive with material removal, FWIW.

I forget who I heard it from, but someone said in a video I watched when I first started turning nearly two years ago, that what matters is the surface speed of the item being turned, not the RPM itself. The larger the radius, the faster the "surface speed" where the tool and material meet. I think, IIRC, the desired "speed" was ~45MPH, which is pretty fast when you think about it! I think I've also heard from Kent Weakley that he prefers lathes without an RPM readout, as it can really bias the turner about what's fast or not. He adjusts the speed until he feels its fast enough at the point of tool to wood contact, which I guess is a sense you have to develop over time (maybe ideally with the help of an experienced turner at first, to give you an idea of whats fast enough vs. too fast or too slow.)

 

[mg_dreyer]

Here is my technique and I try to explain speed and cutting technique -

Click here -> 10 Minutes To Better Pen Making - Turning Acrylic

Hope this helps.

 

[mgoetzke]

1. Are you using a mandrel?
2. What speed are you turning?

These are questions that usually come up way down the line in troubleshooting chip-outs after other suggestions don't match up.

WHY Mandrel question? if the mandrel is flexing, there may be more vibration in the center part. It doesn't take by 1mm flex to create that scenario.
SPEED Question: Too slow can cause a similar chip out. Many times bowl turners will turn much slower than most pen turners. Bowl turning at 12 inch diameter and 700 RPM is MUCH faster cutting speed - than the cutting speed of 3000 RPM on 3/4 inch diameter pen blanks. Too slow will cause catches and chips. It is difficult to move up to 3000 rpm when one has been doing a great job at 700 rpm for a few years.

My answer is different from John Rista's answer. He is referring to tool feed or how much of a "bite" are you taking? My answer is concerning lathe speed. Being too aggressive with the tool can cause flex, and even if no flex is there.

1) Penn State TBC mandrel
2) Around 3000rpm

Seems to happen when I go for that last pass after restarting the lathe. Maybe I'm not addressing the tool correctly?

I just did another blank with just my skew and no issues at all.

 

[jrista]

1) Penn State TBC mandrel
2) Around 3000rpm

Seems to happen when I go for that last pass after restarting the lathe. Maybe I'm not addressing the tool correctly?

I just did another blank with just my skew and no issues at all.

Any chance you could share some pictures of blanks that have had the problem?

Also, how new is your NR carbide tip? A tip with a good, sharp edge does a far better job cutting than a dull one. I ran out of tips a while back with my NR carbide tools, and had rotated through the entire circumference of the last ones, and they definitely don't cut as well as they did at first. When I finally got a new tip, the difference was night and day.

 

[mgoetzke]

Here is my technique and I try to explain speed and cutting technique -

Click here -> 10 Minutes To Better Pen Making - Turning Acrylic

Hope this helps.

Ha - I was trying to copy your technique but I see you hold the tool at an angle to the blank even from the start. I have been trying to keep it perpendicular until it is round then angle it. This could be part of the issue. OK - maybe another problem is on the small round carbide cutter I have the cutter mounted to a self-made bar but haven't added a handle to it yet. I'm using your technique to hold the tool but maybe without the extended handle I don't have as much control?

(edit - I should have asked, the carbide cutters should be cutting right on center?)

 

[mg_dreyer]

Ha - I was trying to copy your technique but I see you hold the tool at an angle to the blank even from the start. I have been trying to keep it perpendicular until it is round then angle it. This could be part of the issue. OK - maybe another problem is on the small round carbide cutter I have the cutter mounted to a self-made bar but haven't added a handle to it yet. I'm using your technique to hold the tool but maybe without the extended handle I don't have as much control?

(edit - I should have asked, the carbide cutters should be cutting right on center?)

Cutter head should always be cutting on the center. Handle parallel to to the ground. The angle you mention are you talking about the 45 degree cut? I do that for two reasons - when rounding i try to go more straight in so that part of the cutter takes the most hits, then the right side 45 with a "sharper" edge, then when I rotate I get a new cutter for the peel cuts.

How are you turning without a handle? I have to have my tool under my arm. Would like to see the handleless hold.

 

[RobS]

Alumilite will also cure differently depending on age, how exact your ratio is, did you preheat your molds, etc.

So it is possible, that the blanks are a little more brittle than normal.

 

[jrista]

Ha - I was trying to copy your technique but I see you hold the tool at an angle to the blank even from the start. I have been trying to keep it perpendicular until it is round then angle it. This could be part of the issue. OK - maybe another problem is on the small round carbide cutter I have the cutter mounted to a self-made bar but haven't added a handle to it yet. I'm using your technique to hold the tool but maybe without the extended handle I don't have as much control?

(edit - I should have asked, the carbide cutters should be cutting right on center?)

I actually learned what I do from Mark @mg_dreyer! ;-) I watched the video he shared....oh, I guess it was a while ago now, but, its what I do. I also hold the tool at an angle. I don't generally take as much material off as he does, maybe I do with with acrylic, but I've never been able to with alumilite. Alumilite, inlace, and trustone, you just have to work it slower, as the material is harder than acrylic, doesn't seem to soften with the heat of friction like acrylic, etc. Polyester is also easier to turn, more like acrylic, but its more sensitive to too much inward pressure from the tool than acrylic is.

Anyway...I find a handle is pretty essential. You want that long lever arm behind the tool rest, so you have fine control of the tool in contact with the blank. With a shorter lever, control is a lot harder. You generally do want the bit to be strait on, and not at an elevated or dropped angle, but with an NR bit a little bit of angle usually doesn't matter. I have found that holding the tool at around a 45 degree angle to the blank just gives me more control.

 

[Hartwell85]

Watch the video that Mark Dreyer posted. It greatly helped me to get better results turning acrylics and Alumilite. Once I get the blank round, I turn to shape between 2,000 to 2,500 rpm. I have found that when turning two acrylic blanks on a mandrel some flexing of the mandrel occurs causing chattering that results in a rough surface. Consider turning one blank at a time using the Turn Between Centers Mandrel System from Penn State.

 

[qquake]

I always trim the corners off before I turn any acrylic. It helps me greatly. Also, I use carbide cutters at an angle so I get a "shearing" cut. That really changed things for me. Now I even routinely turn inlace acrylester blanks with no problems.

 

[mgoetzke]

Thanks for all the help. I rounded two more blanks with my larger NR carbide tool (with super long handle) and all went well. Think my technique approaching the tool perpendicular to the blank was the issue. I angled the tool and the cutting was much smoother.

 

[Displaced Canadian]

I find with carbide tool they work best if you treat them like a skew and have them on an angle. Sharp tools are a must for any type of resin blanks and learning how it feels when all is going well.