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sim · 11-22-2009, 10:37 AM

I got a lathe recently and have been doing a lot of reading but not a whole lot of cutting so far. I'm a bit confused on how to cut a groove on a bar stock. The cutting tools I have so far are a right hand side tool and a left hand side tool.

Seems the advice for turning is to start at the very side (right hand side) of the part, adjust the cutting depth and start feeding. Before I read that, I actually did start cutting from the middle (to avoid the live center) with a right hand side tool and it did sort of work although I wasn't getting a good finish on the part (probably a number of other things I was doing wrong too though) and maybe I even blunted the tip of the tool already.

Do I need another cutting tool if I want to start from the middle?

hellbentrodder · 11-22-2009, 02:43 PM

How wide of a groove are you trying to cut?

Reflection · 11-22-2009, 03:27 PM

What material are you trying to cut?

That will effect the tool your using as well as speeds and feed rates.

A groove on the O.D. or the face of the part is typically done with either a part off tool or a grooving tool. A groove on the I.D. of the part can be done with either a boring bar that's made to hold grooving inserts or a special ground tool. If you have a few tool blanks of high speed steel,you can grind one down to the width of the groove your wanting.

As far as where to start the cut,to avoid having to try and blend,it's best to start at one end and feed the whole pass at once or to the length you need. I would highly recommend using a center drill,making a small center drill hole on the end and using the tail stock if it's a long part. Tool pressure will cause the part to push off. The closer you get to the chuck,the less it will push. Your part will end up having a certain degree of cone shape or taper to it.

Grooving and parting off parts. I like to spin the part about 3-400 rpm's and feed it slow....depends on the O.D. of the part as well. Bigger O.D.'s I'll typically spin the part slower. While parting or grooving,I use a misty sprayer,flood coolant or oil and light compressed air to keep the chips out of the groove. Keeping the groove cleaned out while it's cutting will decrease the chance of a tool breaking 10 to 1. Sometimes I like to feed it by hand while grooving/parting,sometimes I'll use the power feed....just depends on what I'm working on.

chevellian · 11-22-2009, 04:00 PM

You can turn from the middle and work your way to the left and right using the left and right tools. This is not actually grooving.
You can not plunge strait in, you move in the corresponding direction so that the back of the tool does not rub. as you progress you will have an angle on the one side of the cut. Leave .001" from your finish size. Now start turning with the other tool, again leave .001". Now you should have a shoulder on the left and right with a tool line in between. Now use some emery cloth to take down that last .001" and blend out that toolmark.

For grooves, what Reflection said.

sim · 11-22-2009, 05:43 PM

Ah,
Thanks for the replies guys. What chevellian described was what I was trying to do but the other info will also come in handy soon as I do some real grooving. I was mainly trying to turn down some aluminium rods from 8mm to 6mm but the 3-jaw chuck and live centers got in the way, so I was wondering if its okay to just start from the middle instead of the sides. Also, I might try to cut some beadlock rims later since I already have a length of 2.5" diameter delrin bar sitting around.

So I can just start from the middle with a right hand tool and move left and then back the tool out (then do the same with the left hand tool but move right and back out). Do the depths of cuts have to be shallower than normal (where we start from the very end)?

Again, thanks a bunch, guys.
Been reading from Joe Martin's Tabletop Machining and Doug Brinney's Home Machinist Handbook, but some of the more obvious things aren't covered, so its still not easy for a total newbie.

Reflection · 11-22-2009, 06:39 PM

Quote:

Originally Posted by sim

Do the depths of cuts have to be shallower than normal (where we start from the very end)?

Lighter cuts will help as far as the material pushing off. That little 8mm stuff will be real bad to push once you get more than 3" or more away from the chuck.

A part I make quite often at work,starts with .375 aluminum rod. I have to turn it down to .355" Easy enough but the part sticks out of the chuck 4" and it's got a tollerence of +/- .0005" Not to bad on my CNC machine,I can dial it in faster and repeat allot faster. When I make one on a manual lathe,usually the only way is to take .0005" cut each pass,any more that that and it pushes off and kills it.

I've found that sharp tools will help with pushing at times. Dull inserts or lathe bits will push off more so that a sharp cutting edge. If your using the old school style lathe bits,study up and practice on different techniques of putting a good cutting edge on them. Different cutting edges can make a difference with some materials.

chevellian · 11-22-2009, 08:11 PM

Whether you are starting in the middle or from the end really has no impact on the depth of cut. You will need to determine what you can take on roughing passes by trial. The material, tool, lubrication, set-up rigidity and size and precision of the machine all will effect the depth of cut. I take .050" rough passes all the time on our old monarch lathes at work, but on my mini lathe I take around .020" rough passes. Also remember that .020" on your dial will reduce the diameter by .040".

I suggest just turning and facing some scrap to get a feel for your machines capability.

What lathe do you have?

sim · 11-22-2009, 09:06 PM

Mine's just the Sherline 4100 3.5" mini lathe. I know it's not really meant for bars much thicker than 1", but the 2.5" Delrin's just sitting there taunting me every day.

The belts can be changed to a 2nd set of pulleys for a better ratio for low RPM torque.

I was just cutting that aluminium rod for fun more than anything else, but was making some shallow cuts, as I had no idea how far I could push it. My deepest passes were only 0.08mm (about 0.003"). I think I must have taken over an hour to get the diameter down 2.0mm (0.079"). As I didn't know better, instead of backing the tool off at the end of each pass, I moved it back along the Z-axis to get it back to the start, then advanced the depth some more. Probably damaged my cutting tool doing that. Will have to go home and inspect it later.

I need to read up a lot more and start cutting some stuff. You guys have been a great help! Thanks for all the info and for helping a newbie get started in machining.

Reflection · 11-23-2009, 07:53 AM

Quote:

Originally Posted by sim

Mine's just the Sherline 4100 3.5" mini lathe. I know it's not really meant for bars much thicker than 1", but the 2.5" Delrin's just sitting there taunting me every day.

The belts can be changed to a 2nd set of pulleys for a better ratio for low RPM torque.

I'm not sure I'd gear it down for the delrin. You may have to though if the machine doesn't have the sack to spin it. I've never used a lathe like that,so I don't know. Typically plastic cuts better at a faster speed with slower feeds and razor sharp tooling. I'd try it in high gear first.

When I turn the O.D. on delrin here at work,I'll spin it around 1500,give or take a little depending on the size and the tooling I have to work with.

Like chevellian recommended,if your unsure how a certain material will cut,start out small on a scrap piece and see what works best.

sim · 11-23-2009, 11:15 AM

Okay. Will try and turn some scrap Delrin tomorrow and see how it goes. Will try the high speed ratio first since that's what it's on now.

chevellian · 11-23-2009, 05:36 PM

Delrin is wonderful to machine, your mini lathe should be able to handle as big of chunk that fits.

The smaller lathes require that your tool tip be right on center for best results. Set it close with a center in your tailstock, then take a face cut and adjust the tool until it just so takes off the nib at the middle. Also I found that hss works better than carbide on these machines, carbide tends to push a lot more than hss. Your machine, although it is called a mini, is a lot smaller and lighter than my mini, about half the size. I don't think you will be able to achieve the depth of cut that I posted earlier.

Have fun, and be safe!

sim · 11-24-2009, 08:31 AM

Thanks. Will do and will do

dkf · 11-24-2009, 09:25 AM

For a little sherline lathe I'd use only high speed steel tooling because it doesn't apply the cutting force carbide does because it has a sharper edge. I'd pick up a bunch of 1/4" or so HSS or Cobalt square blanks and grind your own tools. Do a search on the net to find how to articles with pics so you get the angles right. When turning plastic its hard to beat a HSS tool with a good sharp edge.

11-22-2009, 10:37 AM	#1
sim Quarry Creeper Join Date: Apr 2005 Location: Malaysia Posts: 374	Cutting a groove with a lathe I got a lathe recently and have been doing a lot of reading but not a whole lot of cutting so far. I'm a bit confused on how to cut a groove on a bar stock. The cutting tools I have so far are a right hand side tool and a left hand side tool. Seems the advice for turning is to start at the very side (right hand side) of the part, adjust the cutting depth and start feeding. Before I read that, I actually did start cutting from the middle (to avoid the live center) with a right hand side tool and it did sort of work although I wasn't getting a good finish on the part (probably a number of other things I was doing wrong too though) and maybe I even blunted the tip of the tool already. Do I need another cutting tool if I want to start from the middle?

11-22-2009, 09:06 PM	#8
sim Quarry Creeper Join Date: Apr 2005 Location: Malaysia Posts: 374	Mine's just the Sherline 4100 3.5" mini lathe. I know it's not really meant for bars much thicker than 1", but the 2.5" Delrin's just sitting there taunting me every day. The belts can be changed to a 2nd set of pulleys for a better ratio for low RPM torque. I was just cutting that aluminium rod for fun more than anything else, but was making some shallow cuts, as I had no idea how far I could push it. My deepest passes were only 0.08mm (about 0.003"). I think I must have taken over an hour to get the diameter down 2.0mm (0.079"). As I didn't know better, instead of backing the tool off at the end of each pass, I moved it back along the Z-axis to get it back to the start, then advanced the depth some more. Probably damaged my cutting tool doing that. Will have to go home and inspect it later. I need to read up a lot more and start cutting some stuff. You guys have been a great help! Thanks for all the info and for helping a newbie get started in machining. Last edited by sim; 11-22-2009 at 09:39 PM.

11-22-2009, 02:43 PM	#2
hellbentrodder Rock Crawler Join Date: Jan 2008 Location: Cotati Posts: 704	How wide of a groove are you trying to cut?

11-22-2009, 03:27 PM	#3
Reflection TEAM MODERATOR Join Date: May 2004 Location: Tennessee Posts: 10,855	What material are you trying to cut? That will effect the tool your using as well as speeds and feed rates. A groove on the O.D. or the face of the part is typically done with either a part off tool or a grooving tool. A groove on the I.D. of the part can be done with either a boring bar that's made to hold grooving inserts or a special ground tool. If you have a few tool blanks of high speed steel,you can grind one down to the width of the groove your wanting. As far as where to start the cut,to avoid having to try and blend,it's best to start at one end and feed the whole pass at once or to the length you need. I would highly recommend using a center drill,making a small center drill hole on the end and using the tail stock if it's a long part. Tool pressure will cause the part to push off. The closer you get to the chuck,the less it will push. Your part will end up having a certain degree of cone shape or taper to it. Grooving and parting off parts. I like to spin the part about 3-400 rpm's and feed it slow....depends on the O.D. of the part as well. Bigger O.D.'s I'll typically spin the part slower. While parting or grooving,I use a misty sprayer,flood coolant or oil and light compressed air to keep the chips out of the groove. Keeping the groove cleaned out while it's cutting will decrease the chance of a tool breaking 10 to 1. Sometimes I like to feed it by hand while grooving/parting,sometimes I'll use the power feed....just depends on what I'm working on.

11-22-2009, 04:00 PM	#4
chevellian Rock Crawler Join Date: Sep 2006 Location: Lititz Posts: 787	You can turn from the middle and work your way to the left and right using the left and right tools. This is not actually grooving. You can not plunge strait in, you move in the corresponding direction so that the back of the tool does not rub. as you progress you will have an angle on the one side of the cut. Leave .001" from your finish size. Now start turning with the other tool, again leave .001". Now you should have a shoulder on the left and right with a tool line in between. Now use some emery cloth to take down that last .001" and blend out that toolmark. For grooves, what Reflection said.

11-22-2009, 05:43 PM	#5
sim Quarry Creeper Join Date: Apr 2005 Location: Malaysia Posts: 374	Ah, Thanks for the replies guys. What chevellian described was what I was trying to do but the other info will also come in handy soon as I do some real grooving. I was mainly trying to turn down some aluminium rods from 8mm to 6mm but the 3-jaw chuck and live centers got in the way, so I was wondering if its okay to just start from the middle instead of the sides. Also, I might try to cut some beadlock rims later since I already have a length of 2.5" diameter delrin bar sitting around. So I can just start from the middle with a right hand tool and move left and then back the tool out (then do the same with the left hand tool but move right and back out). Do the depths of cuts have to be shallower than normal (where we start from the very end)? Again, thanks a bunch, guys. Been reading from Joe Martin's Tabletop Machining and Doug Brinney's Home Machinist Handbook, but some of the more obvious things aren't covered, so its still not easy for a total newbie.

11-22-2009, 08:11 PM	#7
chevellian Rock Crawler Join Date: Sep 2006 Location: Lititz Posts: 787	Whether you are starting in the middle or from the end really has no impact on the depth of cut. You will need to determine what you can take on roughing passes by trial. The material, tool, lubrication, set-up rigidity and size and precision of the machine all will effect the depth of cut. I take .050" rough passes all the time on our old monarch lathes at work, but on my mini lathe I take around .020" rough passes. Also remember that .020" on your dial will reduce the diameter by .040". I suggest just turning and facing some scrap to get a feel for your machines capability. What lathe do you have?

11-23-2009, 11:15 AM	#10
sim Quarry Creeper Join Date: Apr 2005 Location: Malaysia Posts: 374	Okay. Will try and turn some scrap Delrin tomorrow and see how it goes. Will try the high speed ratio first since that's what it's on now.

11-23-2009, 05:36 PM	#11
chevellian Rock Crawler Join Date: Sep 2006 Location: Lititz Posts: 787	Delrin is wonderful to machine, your mini lathe should be able to handle as big of chunk that fits. The smaller lathes require that your tool tip be right on center for best results. Set it close with a center in your tailstock, then take a face cut and adjust the tool until it just so takes off the nib at the middle. Also I found that hss works better than carbide on these machines, carbide tends to push a lot more than hss. Your machine, although it is called a mini, is a lot smaller and lighter than my mini, about half the size. I don't think you will be able to achieve the depth of cut that I posted earlier. Have fun, and be safe!

11-24-2009, 08:31 AM	#12
sim Quarry Creeper Join Date: Apr 2005 Location: Malaysia Posts: 374	Thanks. Will do and will do

11-24-2009, 09:25 AM	#13
dkf Rock Crawler Join Date: Apr 2009 Location: Pa Posts: 563	For a little sherline lathe I'd use only high speed steel tooling because it doesn't apply the cutting force carbide does because it has a sharper edge. I'd pick up a bunch of 1/4" or so HSS or Cobalt square blanks and grind your own tools. Do a search on the net to find how to articles with pics so you get the angles right. When turning plastic its hard to beat a HSS tool with a good sharp edge.

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