New Lathe: New Problems

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hesperaux

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Sep 8, 2024
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5
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Illinois
Hello all,

I'll start with some background info, but the short version is: when I put a piece of delrin into my new wood lathe, it wobbles like crazy no matter what I do, but the headstock, collet chuck (MT2 mounted), and 4-jaw scroll chuck all measure a TIR less than 2 thou.

I have some beginner level experience with the mill and the metal lathe; mostly the mill. I've turned a couple of things on the metal lathe but I'm fairly inexperienced with turning. As part of starting into a new fountain pen hobby and wanting to start turning them myself (bespoke ones, to be clear), I have purchased an entry level midi-lathe. It is a 6x12" WEN without speed control.
In addition, I also purchased a couple of carbide carving tools and a 4-jaw scroll chuck from Amazon. It's a Chinese brand (Deefine) nickel plated chuck that comes in a case with 4 different jaw sets. It seems fine..?

With all that said, I have been trying to rough cut a short piece of delrin (about 1 inch stickout). I actually roughed it down to about 750 mils diameter in the metal lathe first, to try cutting it on the wood lathe with the collet chuck. I quickly realized that I needed a drawbar to hold the collet chuck in (more on that later) and figured that my wobble was caused by that, so I switched to the 4 jaw and mounted it into the pin jaws (not PEN, pin).

No matter what I do, I cannot get the pin jaws to grab the part square. So I gave up and just tried to see if I could rough the piece again to square it. And that doesn't work either. I'm using a square carbide insert in my chisel and no matter how long I wittle away at the workpiece, it continues to chatter. I'm running the lathe at its slowest speed for now (about 520rpm). When I mount the workpiece I can visibly see it wobbling - it is crazy. Maybe I just didn't cut enough off for it to straighten out, but I feel like I really laid into it. I probably cut off at least 50 or 100 thou.

I double checked the chuck jaw attachments (the plates that screw into the jaws), making sure they were screwed in correctly, etc. And I've never removed the actual jaws from the chuck - it is brand new as of yesterday. They appear to have been installed correctly, in the correct order. I also made sure the attachment numbers matched the jaw numbers.

Finally, I measured the runout with a DTI of the outer diameter of the chuck after screwing it onto the head stock. I also measured the interior of the spindle taper with the chuck removed. Both were around 1.5-2 thou. Later, I inserted a smooth piece of hardened tool steel rod into the chuck and measured the runout on it (length of about 2-2.5 inches). I measured about 6 thou. Not great, but it probably wasn't straight or maybe the random piece I pulled had imperfections.

I noticed that the jaw fingers for the pin jaws are serrated, so I thought maybe they were biting into the delrin and not allowing it to straighten out, so I went back to the collet chuck to see if I could get that to work. I found some appropriate threaded rod to screw through the headstock bore, and double nutted the back of the rod inside the hand wheel, screwing the whole thing into the collet chuck taper. Basically, a poor man's draw bar. But it still chatters like crazy when I try to rough cut the delrin.

Sorry for the long explanation, but I'm at my wit's end. I have no idea why I can't get this piece to go straight - it works fine in my metal lathe with the three jaw chuck. I am a noob to wood lathes. Am I doing something stupid? Did I buy a piece of junk chuck? (It was like a $160 kit on sale). I regret not having looked into it more, cuz I would've just bought a Nova set, but the mistake has been made.

Tomorrow (I'm up late at 7:30AM and about to go to sleep), I'm going to pop the collet chuck back out (it's pretty stuck in there..), put a piece of scrap wood in, and start with a fresh cut between centers. If that works, I'll take the live center out and see if it spins true in only the chuck. If all goes well, I'll get a fresh piece of delrin and try that as well.

But in case that doesn't work out, can anyone advise what might be wrong? Thanks a lot for taking the time to read all of this. I do not have the capability of being succinct. >:D



-David
 
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These may be obvious and just an opinion, but I did not see it in your details. Make sure you are supporting your workpiece with a tailstock live center. Delrin is very flexible, and I find that working with it without tailstock support, it always goes wonky on me. This should lessen the chatter when turning. Make sure your tool is sharp so that you are not putting too much pressure on the cut to bend the workpiece. Also, I feel that you are turning too slowly. I would double or triple your lathe speed. It may be your chuck, but I would try these if you haven't thought of it yet.

Good luck!
 
Let me try to summarize the pertinent facts:

When you run the lathe with nothing attached to the headstock spindle, the runout is negligible. When you attach the four-jaw chuck, the runout increases, but is still relatively insignificant. But when you try to mount a delrin blank in the scroll chuck, you get significant wobble.

Presumably, the blank initially had a rectangular cross section. In that case, mounting it in a four-jaw chuck would inevitably result in some wobble because it would be difficult to grip a rectangular blank with a chuck that was designed to hold something round and getting the center of mass directly on the axis of rotation. That's a common situation, and the usual solution is to just turn the portion of the blank that extends out of the chuck to round, then flip it end for end and remount the now rounded portion in the chuck, and round off the remained of the blank. Or, you could mount the blank between centers and round over the entire length. Either approach works - I have done it both ways depending on the size blank, and what I feel like at the time.

But you said that you tried turning the blank to round on a metal lathe before transferring the now-round blank to the wood lathe scroll chuck), and it still wobbled. Did you mark centers on the blank before rounding it over, and were those centers still on-axis when you remounted it in the wood lathe scroll chuck?

By any chance, have you checked to make sure that the jaws are properly mounted on your scroll chuck? Scroll chuck jaws are numbered, and must be installed on the chuck sliders with corresponding numbers. If the jaws aren't properly attached to the chuck, anything mounted in the chuck will be off-axis. A quick check is to close the jaws -- if all four jaws reach the center at the same time as the jaws close, then they are properly installed. But if the four jaws do not touch when the chuck is fully closed, then something is wrong.

[Sorry - I reread your post and realize that you did check that the jaws are installed properly. But it would still make sense to try closing the chuck to confirm that all four jaws reach the center simultaneously. That would rule out any serious defect in the chuck.]

Can you post some pictures of your setup? Perhaps with the blank in place in the scroll chuck?

And one other question - when you round over the blank in your metal lathe and then remount it in the scroll chuck, how much wobble are you seeing? Specifically, is that wobble limited to the blank itself, or is the entire lathe wobbling? If the entire lathe is wobbling, have you checked that it is properly leveled on your bench?
 
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So much going on here but delrin can be flexible and can bend easily. But the thing is start by turning it between centers on the wood lathe. That should get you a cylinder to work with. It also gives you the center points on both ends. Now you said you want to cut a piece off. How large of a piece? As I said that stuff is not meant to be used in long lengths on a lathe. It is too flexible. But having said that your collet chuck is the best chuck to chuck it up in. It should be able to grip the round bar now and slide the tailstock up to the center point and cut a slice off. Yes On speeding the lathe up.
 
My initial thoughts were all related to the tool rest and how the tool is held.

1) Keep your tool flat on the tool rest. No angles, no tipping the bar to the side. Keep it flat on the rest for the safest and cleanest cut.

2) Hold the tool horizontal, parallel to the floor for the best control of the tool.

3) Always keep the tip of the tool on the center line of the workpiece - or just slightly above center. Although I have made a quick setup gauge for mine, I initially set it by adjusting things using the point of a dead center as the location of the center line. SImply put, shorten the tool overhang as much as possible.

4) Make sure your tool rest is correctly positioned to address #1 through #3 and also make sure your tool rest is positioned as close to the workpiece as possible while having the heel of your tool resting on the tool rest while having the cutting edge of the carbide to reach the workpiece.

I hope you find a technique and setup that works well for you. - Dave
 
520RPM?
1. This isn't a metal lathe;
2. You are not turning 12" or 14" bowls. Large diameter bowls go at slow speeds but 1 inch and 3/4 inch diameter turnings need 2000 rpm or more to get similar cutting speeds of 14" bowls at 500 rpm.

The slow speed is causing the tool to just whack at it. A diagram I have posted several times over the years gets overlooked as it relates to speeds, but slower speeds on wood and soft material can cause chatter or splintering as in the photo below. Notice the rougher drill cuts at 620rpm vs 3100 rpm.
www.penturners.org

Drill_Bit_Speed.png

Drill bit speeds
www.penturners.org

Yes, that is a drill bit, but the difference in cutting at different speeds becomes evident. With metal or machinist lathes, metal cutting causes intense heat with higher rpm. Their inherent precision and hardness of cutting tools allow slower turning speeds and require cooler turning (slower rpm) versus high speed turning. However, in wood or delrin, heat build up from the cutting edge and speed is not a huge problem for them, therefore, speed it up.
 
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You guys are awesome. Thank you so much for all the replies.

I feel really stupid now, cuz I took that little stub piece I've been testing with, turned the lathe up to 1400rpm, and it worked..... I had no idea the speed mattered THAT much. I guess the tool tends to bounce more at slower rpms?

I also noticed that I have a few small chatter marks even at the high rpm but that's just my lack of skill with the chisel and how close it was to the chuck (which makes me skittish). I am used to metal machining and I think this will be a really fun journey.

That being said, all the advice is great to have and it's duly noted. I am really excited now because I think I can finally get started finishing up some mandrels and get on to pen turning.

Thanks again! You guys are awesome. Thank you for being gentle. I am gonna post another thread about nib sourcing too. 😃
 
hesperaux said:
I feel really stupid now,
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Feel good that you're asking for advice. There are no mistakes..they are learning experiences. It's important to execute , observe and adjust. Get started, see what happens and make corrections.
hesperaux said:
Thanks again! You guys are awesome. Thank you for being gentle. I am gonna post another thread about nib sourcing too. 😃
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Great group of members. They share..they do not bash, insult or make anyone feel bad. Most members have a lot of regard for other members. Everyone was a beginner. Welcome aboard. Safety first and have fun.
 
If your background is metal lathe work, a wood lathe will probably appear very wobbly.

Also you mention a square carbide cutter. Carbide cutters are great, but there's a learning curve with each shape.
With the exception of parting tools, I only turn with carbide.

If it's a straight square, it is a very difficult insert to use with consistent results. To me, it is mainly for turning fine detail and doing convex rounded shapes. If you let the entire side contact the workpiece, chances are that it will chatter and tear off chunks of the material. Either use the pointy bit for rough shaping with sliding cuts, or use the long side against a convex surface (in which case only a small point of the long side is in contact).

If it's a convex-side square type, then it's a lot more beginner-friendly than a straight one, but I find that it's not as good as either the round bit or the straight square bit in respective applications. Never found a good use for it apart from initial roughing of very dense materials.

The main go-to cutter is 16-14mm round bit - that's the one I'd start with.

Carbide does not produce a good surface and requires sanding with an 80 or 120-grit start. Absolutely not an issue for small , high-polish items like pens or chessmen, but for bigger work that can be a lot of sanding, which is why a lot of turners look down on carbide.
 
On forums like this, I feel like I'm not supposed to keep the conversation going once the issue is resolved, but a few of you responded so I'd like to say a few other things.

mChavez said:
If your background is metal lathe work, a wood lathe will probably appear very wobbly.

Also you mention a square carbide cutter. Carbide cutters are great, but there's a learning curve with each shape.
With the exception of parting tools, I only turn with carbide.

If it's a straight square, it is a very difficult insert to use with consistent results. To me, it is mainly for turning fine detail and doing convex rounded shapes. If you let the entire side contact the workpiece, chances are that it will chatter and tear off chunks of the material. Either use the pointy bit for rough shaping with sliding cuts, or use the long side against a convex surface (in which case only a small point of the long side is in contact).

If it's a convex-side square type, then it's a lot more beginner-friendly than a straight one, but I find that it's not as good as either the round bit or the straight square bit in respective applications. Never found a good use for it apart from initial roughing of very dense materials.

The main go-to cutter is 16-14mm round bit - that's the one I'd start with.

Carbide does not produce a good surface and requires sanding with an 80 or 120-grit start. Absolutely not an issue for small , high-polish items like pens or chessmen, but for bigger work that can be a lot of sanding, which is why a lot of turners look down on carbide.
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You're absolutely right about this. I switched from the square to the circular cutter and it is a dream to work with. I have still been using the diamond and the square for certain things but the circular cutter makes a huge difference. I was getting an incredible surface finish, as well, which surprised me. I went to sand it after and it made it look horrible, lol. I need to learn how to sand/polish properly still.

Just for having a little more variety in shapes (I still feel a little lacking with the circle, square, and diamond carbide tips), I went ahead and got a set of HSS chisels, including a parting tool, which I was lacking (the diamond works but it grabs very easily if you aren't careful).

d_bondi said:
David,

If you continue to have chatter issues with the tools, consider getting yourself some negative rake cutters, they make a big difference when turning synthetics.

David
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I did look into some negative rake tools after reading your comment. However, because I was a cheapskate with my carbide tool set, I was not able to find inserts with a negative rake that would fit. At least, based on measuring the inserts I have and looking around. But as mentioned above, the circle tool is really helping reduce the chatter now.


I've been working the past two days on making mandrels and my first fountain pen. I was partially successful. I was a derp and accidentally made the cap too short, but I was kinda winging it. I made a working section and body, which is great progress in my opinion. The cap works too but I didn't shape it since the drill popped right out the top. I could salvage it later by adding a finial and maybe a clip, but for now I will remake it.
I've gotten much more familiar with how the wood lathe feels and how to use the rest and the chisels a bit better. I'm enjoying the process, even if my back pain is not.
I have noticed something strange, though. When I use my live center, I get butter smooth cuts on the 50% of the work piece that is closer to the live center, but the half that is closer to my collet chuck screetches, rumbles, and chatters more. I'm guessing this could be due to the live center allowing for a little play in the part? Maybe my workpiece is not straight in the collet and is bending towards the live center (they're not aligned)?

Any advice on what to check for this issue would be helpful. I'll also mention that the issues even show up on short pieces that are supported (about 2" sections of delrin).

Kind regards,
David
 
Sounds like chuck runout. Shouldn't be the case with a collet chuck, unless your blank is not clamped straight.

Round, square and diamond is all you need. Having small round and large round helps if you get into finer, more creative work like chessmen or jewellery. Plus HSS parting tools in different sizes (I have 2mm, 4mm and 6mm).

Sounds like you already have more custom pen making experience than me :p. I'm still waiting on some tooling, because the stuff I had lying about is not well suited for this job. The postie's running late - it could be that the pre-Christmas jitters have started already.
You'll be pleased to know, my lathe's probably worse than yours. ;)
 
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Agreed - I ran an indicator on it but not since I first was messing with the chuck. I'll do another measurement for runout soon. Busy work week ahead so I'll probably not get to it until the weekend.
When I finish my first pen, I'll be sure to share it on the forums here for posterity :)

I couldn't believe how much money I just spent on all this stuff, but I think it will be worth it. I have already really been enjoying the process, even though I am failing so far. It is fun and there are small victories!
 
I just have to chime in one more time regarding speed. I might run my lathe a little slower until my blank is round, but then I crank it up to 3600 RPM to turn pens. I use my round carbide to get down to nearly the final shape and then I finish with my square-rounded corners cutter to smooth everything out. I sand at about 1000 RPM starting with 400 grit because the square cutter leaves a nice smooth surface. I apply standard CA finishes at about 500 RPM, Doctors Woodshop at a higher speed according to the Doctors directions, and for GluBoost I haven't quite figured that out yet, other than between slow and no speed. I MicroMesh at about 1000 or use Magic Juice at about 3000 for polishing.

Developing a good, solid regimen that produces good and repeatable results is half the fun.

Good luck on your journey. It can be very rewarding.

Dave
 
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