Mini Lathe Tool Lifting, Should I Remove the Compound Rest?

[jtrout13]

I am having issues with my mini lathe tooling wanting to 'lift' when I try to take cuts that are the least bit aggressive.

Here's my current setup: I've put tapered gibs on the carriage and the cross and compound gibs are tight. I've got the compound set at 0 degrees (parallel to the ways) and locked, and I'm using a QCTP. By an 'aggressive' cut, I mean this setup to face off some A2 drill rod 3/4" dia, 400 RPM with HSS, 0.005" DOC (facing using a right hand tool from the inside out, as this piece has a through hole on it).

The QCTP is bolted securely to the compound. I can't determine if the flex/lift is in the compound-qctp joint, or if it is in the compound itself. I wondered if any other mini-lathe users could offer advice. I know many of you remove the compound and replace it with a solid block, but that's really not the ideal solution for me, because I like the utility of having the compound on there. However, I don't want to keep dealing with this issue. Is this the type of situation which would be remedied by removing the compound?

EDIT: I'm also thinking maybe if I mount the compound at 30deg instead of 0deg that more of the force will be transmitted along the axis of the compound leadscrew, and then I can just dial in the compound twice the distance I want to move it along the ways, when I'm using the dials for facing to a predetermined length... Ideas?


Thanks, John

 

[vigsgb]

This seems like a silly question as I am pretty new but if the tool is lifting would that imply you may be going the wrong way on the spindle?

Maybe I don't understand what you mean by lifting.

 

[Sshire]

This is a common issue with many 7x,9x and some 10 and 11x lathes. Google "4 bolt compound fix" or something like that. you'll find a lots of posts in various forums for the procedure. It seems to solve your problem. I'll check my bookmarks and see if I can come up with it.

 

[Sshire]

Steve Bedair's website here

http://bedair.org/clamp/9x20clamp.html

 

[cfellows]

John,

First, when you say mini lathe, I assume you have a 7 x 10 or variant with two bolts holding the compound to a swiveling disk in the carriage?

Also, when you say "lift", where exactly are you seeing the lift?

As a first shot, I would try setting the compound perpendicular to the lathe ways and see if that helps or eliminates the problem.

Let us know what you find.

Chuck

 

[jtrout13]

Chuck, You're right, I have the 7x16 from Micro-Mark. I see the lift at the tool tip, when the tool first bites into the material the tool will 'lift' to avoid cutting, then it will eventually start cutting. I can't determine if the problem is in the toolpost or is in the compound. However, the toolpost is attached quite rigidly. I think possibly the swiveling disc under the compound is the weak point.

I'm going to first try setting the compound perpendicular to the ways and see what happens. If that doesn't work I'll move further. I suppose I could replace the compound with a block, but I like having the compound, and I think lathes are supposed to have one. I'm spending a lot of time putting power feeds on all axes and DRO like all the 'big machines', so I want my little lathe to have a compound if at all possible.

Also for you Chuck, I read your thread about how you built the tangential toolpost for your mini lathe, which eliminates the compound. Could you elaborate a little more on what kind of issues led you to remove the compound?

 

[Don1966]

I have the Micro Mark lathe and the same has happen to mind. You have to adjust the gibs on the under carriage also. I refitted the compound slide and cross slide with bigger gib adjust screws this helps a lot. But the Chinese lathe will not give you any better results without lapping the slide. I passed a stone to remove the burs on the slide ways and v,s on the cross slide and compound slide.
But if you check the carriage gibs I am sure you will find them hard to adjust and loose. Do not over tighten these or you will break the gibs. Follow the books to adjust.
On another point the lathe is not very rigid and you will remove some of the movement, but not all.
I also would like to add, you must set the cutting tool to center height.

Don

 

[MachineTom]

The geometry of the bit sounds that it isn't correct. There needs more relief on the tip/nose of the bit, and maybe increase rake. How abouut a shot of your tool cutter. You should face from outside in, but in this case it isn't an issue. I don't see this as a lthe problem, its the tool bit.

 

[kf2qd]

I have a 7x10 that I have abused in all manner of ways and have never had that problem. It would seem to me that your cutter is lacking in clearance (I use cutters with a completely flat top, no rake)

 

[jtrout13]

Thanks guys, I will experiment with different tooling and compound angles to see what happens.

 

[cfellows]

Chuck, You're right, I have the 7x16 from Micro-Mark. I see the lift at the tool tip, when the tool first bites into the material the tool will 'lift' to avoid cutting, then it will eventually start cutting. I can't determine if the problem is in the toolpost or is in the compound. However, the toolpost is attached quite rigidly. I think possibly the swiveling disc under the compound is the weak point.

I'm going to first try setting the compound perpendicular to the ways and see what happens. If that doesn't work I'll move further. I suppose I could replace the compound with a block, but I like having the compound, and I think lathes are supposed to have one. I'm spending a lot of time putting power feeds on all axes and DRO like all the 'big machines', so I want my little lathe to have a compound if at all possible.

Also for you Chuck, I read your thread about how you built the tangential toolpost for your mini lathe, which eliminates the compound. Could you elaborate a little more on what kind of issues led you to remove the compound?

I didn't really have any issues. I just rarely use the compound and it uses up a lot of real estate on the carriage. Also, I figured removing the compound would make everything that much more rigid.

Regarding our lift problem, it sounds to me like your tool tip is too high. Have you tried lowering it some to see if that helps?

Chuck

 

[cfellows]

Further to my last post, see the attached picture. I'm wondering if your setup is like the top picture where the tool tip is riding slightly above the centerline of the work. Try lowering it to or slightly below the center line, like the bottom picture, and see if that helps.

 

[ninefinger]

I just reread your original post after reading Chucks and I now think I've put together what is happening. As you are facing from INSIDE to OUTSIDE you are getting tool lift due to insufficient front clearance. The bottom of the tool bit is contacting the inside radius of the cut as you try and feed outward. So you have 2 simple solutions:
1. Face from outside to inside
2. Grind the bottom and face of your tool bit to clear the material as you approach the cut from the inside.

Cutting from the inside is similar to boring so
a) you actually may want the tool slightly above the center line so that as it deflects it either takes less of a cut / doesn't dig in and take more of a cut
b) relieve the front of the tool to remove the interference. I'll try and create a simple graphic to explain

Mike

 

[jtrout13]

Guys, you're right. I tried today using some brazed carbide bits (unhardened steel shank) in the same setup, and got the same issues. When I looked at the end of the tool, the drill rod (harder even in annealed state than the shank of the brazed carbide tool) had worn away some of the shank, indicating I need more front clearance.

As for facing from inside-outside, I find for bored parts it is easier and requires less pressure on the tool, as well as leaving a much better surface finish.