I have been using my lathe a lot and was getting pretty comfortable with hitting my dimensions. It has been confidence inspiring until today when I began having trouble taking small cuts to hit my mark. It's the first time that I couldn't dial in another 1 or 2 thou without the dial pushing back a bit. I have a new cross slide screw and nut and this just started happening. What should I be checking on my lathe?
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Springback in Cross Slide
- Thread starter Kevin T
- Start date
- Replies 33
- Views 3,122
iwananew10K
Diamond
- Joined
- Sep 12, 2010
- Location
- moscow,ohio
sounds counterintuitive but small cuts can be a problem in and of themselves.
takes a certain ammount of pressure to initiate a cut.
the smaller the cut the more imperitive it is to have truly sharp tools.
geometry matters as does the actual edge.
suggestions-
examine your cutting edges under magnification.
also fix an indicator to the bed and put the tip on your toolholder...then use your finger to push imitatating cutting pressure....you may be surprised how little pressure it takes to move that needle.
takes a certain ammount of pressure to initiate a cut.
the smaller the cut the more imperitive it is to have truly sharp tools.
geometry matters as does the actual edge.
suggestions-
examine your cutting edges under magnification.
also fix an indicator to the bed and put the tip on your toolholder...then use your finger to push imitatating cutting pressure....you may be surprised how little pressure it takes to move that needle.
Thank You! I used the heck out of a small bit in a boring bar today and it was towards the end of the day, after much material removed. I have been cleaning up my cutters on oil stones prior to starting but today was a long day.
BUT.. the dial moving back was before any load on the cutter.
iwananew10K
Diamond
- Joined
- Sep 12, 2010
- Location
- moscow,ohio
it can also be helpful to have dedicated roughing and finishing tools.
i know for me at least i was guilty of dinking around with way too many little cuts when i was starting out....very often the case is deeper cuts and higher feeds are the order of the day.
old machines like slow speeds,big bites and higher feeds...makes em feel relevant.
i know for me at least i was guilty of dinking around with way too many little cuts when i was starting out....very often the case is deeper cuts and higher feeds are the order of the day.
old machines like slow speeds,big bites and higher feeds...makes em feel relevant.
it can also be helpful to have dedicated roughing and finishing tools.
i know for me at least i was guilty of dinking around with way too many little cuts when i was starting out....very often the case is deeper cuts and higher feeds are the order of the day.
old machines like slow speeds,big bites and higher feeds...makes em feel relevant.
So are you saying there was built up interference (tension) in the screw and nut from prior passes with a dull tool?
iwananew10K
Diamond
- Joined
- Sep 12, 2010
- Location
- moscow,ohio
not so much that directly.
more just an artifact of cutting tools dulling as they are being used requiring more and more cutting pressure.
thus the usefulness of a dedicated roughing tool to remove the meat....plow it off then switch to your finisher.
more just an artifact of cutting tools dulling as they are being used requiring more and more cutting pressure.
thus the usefulness of a dedicated roughing tool to remove the meat....plow it off then switch to your finisher.
pavt
Stainless
- Joined
- Jun 30, 2013
- Location
- 20 miles north of Buffalo NY
Actually this has been helpful to me, in that I am re-considering my grinding style. In the spirit of keeping things simple, I tend to use a flat top, neutral rake. I do have a couple of tools with very high positive rake for tough jobs, and I know the machine works a lot easier with them.
SLK001
Stainless
- Joined
- Feb 8, 2015
- Location
- Coral Springs, FL USA
With a flat rake, you are scraping the material off. With a positive rake, you are shearing the material off.
Richard King
Diamond
- Joined
- Jul 12, 2005
- Location
- Cottage Grove, MN 55016
If you replaced the screw and nut, did you remove the cross-slide? I bet you did and you may have tightened the gib to much and the push back is because the cross-slide isn't sliding a head as it should. Are you using way oil? Did the ways look super smooth? Did you stone the ways? How are you lubricating the cross-slide? When you crank the slide toward the operator side does it get hard to turn with the gib loose? The nut maybe in a bind if it the center-line is not the same. How worn are your ways? If your not grinding the side rake (top) tapering down to right and the lathe saddle and cross-slide are worn out low toward the chuck the tool maybe a negative and the tool is pushing back. What type of tool holder are you using?
Last edited:
Richard King
Diamond
- Joined
- Jul 12, 2005
- Location
- Cottage Grove, MN 55016
I pulled out a Text Book.."Machine Tool Practices" sorry it's sideways...lol
jim rozen
Diamond
- Joined
- Feb 26, 2004
- Location
- peekskill, NY
You don't say what lathe this is, but: check the attachment between the crossfeed nut and the slide. On the smaller
lathes it's a odd screw/cross pin deal, on the larger ones the nut is held with that strange screw with the oiler port in the
top. If the nut comes loose you can see your effect.
Also some of those nuts never had the oiler hole drilled all the way though. The oil level never goes down!
lathes it's a odd screw/cross pin deal, on the larger ones the nut is held with that strange screw with the oiler port in the
top. If the nut comes loose you can see your effect.
Also some of those nuts never had the oiler hole drilled all the way though. The oil level never goes down!
iwananew10K
Diamond
- Joined
- Sep 12, 2010
- Location
- moscow,ohio
i just reread....do you mean the dial itself is moving back??
if so check the slotted nut.
if so check the slotted nut.
michiganbuck
Diamond
- Joined
- Jun 28, 2012
- Location
- Mt Clemens, Michigan 48035
Agree some positive rake for side cuting edge and back rake for steel turning and threding, fingernail shaving sharp edge, clearance under the cutting edge about 9 to 12* , the point radius not following the intersect of side and flllow grind but it also at about 8 to 12*..tool bit/insert near center of part and bit/insert held short.
And this could be the problem.. the tool holder should be set a little more towards center of your compound to make everything more solid....set way left it can try to tip it to take up all the slack in your gibs, so not pushing straight down solid. guess you could mount an indicator at some place to see if your tool holder or compound is tipping when your are in a cut.
Yes perhaps your gibs have .002 clearance and so the cutting force tries to tip it .002 before becomimg solid and doing the work in that position. Then at a light pass with little pressuer so it does not tip..
I see a lot of of YouTubbers doing the far/far left thing. Guess they learned that in high school shop class to avoid bumbing the chuck and never learned better. .
*Tool bit/insert attitude is very impotant. *should have this posted near your lathe..
https://littlemachineshop.com/images/gallery/instructions/grindingtoolbits.pdf
And this could be the problem.. the tool holder should be set a little more towards center of your compound to make everything more solid....set way left it can try to tip it to take up all the slack in your gibs, so not pushing straight down solid. guess you could mount an indicator at some place to see if your tool holder or compound is tipping when your are in a cut.
Yes perhaps your gibs have .002 clearance and so the cutting force tries to tip it .002 before becomimg solid and doing the work in that position. Then at a light pass with little pressuer so it does not tip..
I see a lot of of YouTubbers doing the far/far left thing. Guess they learned that in high school shop class to avoid bumbing the chuck and never learned better. .
*Tool bit/insert attitude is very impotant. *should have this posted near your lathe..
https://littlemachineshop.com/images/gallery/instructions/grindingtoolbits.pdf
mcload
Hot Rolled
- Joined
- Nov 5, 2007
- Location
- Houston, Texas
Yes the dial. I was setting up for the next pass (no load) with the dial and it turning it to the desired depth it would not stay on the mark. It would "spring back" about .0015 on the dial. Thanks for re reading these were finishing passes for a slip fit ID so kinda critical and I had done the same operations a few days ago with none of this going on.
All of this sounds most plausible, since I had it apart. Thanks! I am really good about lubrication but...the way oil on cross slide....The part I can see always gets oiled but I have been lazy about not extending the travel to the extents for application. Actually just dawned on me thinking about extents, I have been using the lathe a lot and generating a lot of chips maybe some got lodged somewhere? I'll pull the cover off and check that too. And the tension on the crosslide adjustment too. Thanks, I understand these suggestions!
Oh and I'm presently using the lantern tool post. The bugger of it was that I made this same part last week with none of the issues. This was at the end of a long day of machining for me and the machine. I didn't take a picture of the cutter but it was the finishing passes on the 1.405 ID x 2.1 depth. Here's the set up, 1.0 dia boring bar operation where I had opened up the ID of the chucked part.
I "think" I got all this part right based on the chips and the fact that I had already made the part once.
texasgeartrain
Titanium
- Joined
- Feb 23, 2016
- Location
- Houston, TX
If a gibs issue, after adjusting, might check the set screw and the tiny brass slug that tightens on thread of adjusting screw.
Not just on lathes, could be a mill or anything. But a lot of machines would use a wiper or a guard for a dovetail exposed to chips. These compound rests don't. In certain things I might be doing, I might cut cardboard shields or deflectors. Maybe use masking tape to help. If I'm thinking of it, I do it for ways too just for ease of after action clean up.
Not sure a chip is your problem, just a thought.
Not just on lathes, could be a mill or anything. But a lot of machines would use a wiper or a guard for a dovetail exposed to chips. These compound rests don't. In certain things I might be doing, I might cut cardboard shields or deflectors. Maybe use masking tape to help. If I'm thinking of it, I do it for ways too just for ease of after action clean up.
Not sure a chip is your problem, just a thought.
I have been using cardboard strategically but I am getting lazy with it and want to make something to guide the chips and oil where I want it to go. On my last lathe I made a brass deflector that worked really well.
I just went through the cross slide and it was definitely dry at the far end. It's not easy to get way oil down there with the taper cover on but I can do a better job of it for sure. Loosened up the gib a little too. It will be a bit before I can test it out, I ran out of material to turn!
texasgeartrain
Titanium
- Joined
- Feb 23, 2016
- Location
- Houston, TX
Just so we're on the same page with terminology. Are you referring to cross slide as compound rest, or the compound itself with cross feed screw. Which dial had spring back ?
If the crossfeed itself, there's a number of considerations for you. You have taper attachment. Locking handle on taper attachment should be loose with slot moving free on stud of locking handle.
Without a shield on that slot, chips can get on crossfeed screw. If you think an issue there, it'd only take a few minutes to remove that handle and two bolts holding to compound. Check and clean crossfeed screw.
If the crossfeed itself, there's a number of considerations for you. You have taper attachment. Locking handle on taper attachment should be loose with slot moving free on stud of locking handle.
Without a shield on that slot, chips can get on crossfeed screw. If you think an issue there, it'd only take a few minutes to remove that handle and two bolts holding to compound. Check and clean crossfeed screw.
michiganbuck
Diamond
- Joined
- Jun 28, 2012
- Location
- Mt Clemens, Michigan 48035
I Did not know you were boring...for boring rake angles are also important..
*But very important is the clearance below the cutting edge. You can hold the boring bar bit/insert in a size hole and see there is clearance below the edge and around that radius all the way to the bottom of the heal.
I have drawn the tool bit and the bore at 10x scale to see and to be sure clearance to all the way down and around.
I have seen tool setup where the bit had to force the tool down /twist to make a cut.
Any lack of clearance will cause the heal to bump and try to push the cutter/bit/insert away.
It is not uncommon to need 3 or 4 different clearance angles or a radial relief below the cutting edge on a boring operation.
If the chip seems thicker than your feed amount the material could be compacting. so, a little top rake may be needed, some axial back rake can aid a boring operation, so sloping down from the feed direction.
Drawing/sketch...Say you start with a 3/4" bore on your part. So, draw a 7 1/2" circle. Then draw in your bit to scale at part ID centerline to see whet clearance angles below the cutting edge are needed.
*But very important is the clearance below the cutting edge. You can hold the boring bar bit/insert in a size hole and see there is clearance below the edge and around that radius all the way to the bottom of the heal.
I have drawn the tool bit and the bore at 10x scale to see and to be sure clearance to all the way down and around.
I have seen tool setup where the bit had to force the tool down /twist to make a cut.
Any lack of clearance will cause the heal to bump and try to push the cutter/bit/insert away.
It is not uncommon to need 3 or 4 different clearance angles or a radial relief below the cutting edge on a boring operation.
If the chip seems thicker than your feed amount the material could be compacting. so, a little top rake may be needed, some axial back rake can aid a boring operation, so sloping down from the feed direction.
Drawing/sketch...Say you start with a 3/4" bore on your part. So, draw a 7 1/2" circle. Then draw in your bit to scale at part ID centerline to see whet clearance angles below the cutting edge are needed.
