# A Short Note About Holding Cutting Tools On Small Lathes



## randyc (Feb 7, 2015)

Here's a simple sketch, familiar to most of us, showing the cutting force applied to the tip of a lathe cutting tool and the resulting (exaggerated) "tipping" of the compound, cross-slide and carriage of the lathe.  The cutting tool drops below the center line momentarily as the structure flexes and then lifts, depending on speed, feed and setup rigidity, then the tool returns to the normal position.  The process becomes repetitive and we have "chatter" which occurs in cut-off situations with small lathes (or during heavy cuts).




  Machinists and most hobbyists with a few years experience have a good grasp of this so perhaps the post can be considered as "light entertainment", LOL.

  Most small lathes are delivered with four-way toolposts and these can be satisfactory if the dimensions are appropriate to the compound mounting surface.  In my experience, most operations required by the compound slide require setting the compound angle between 25 and 45 degrees.  But when adjusted in that manner on a small machine, the four-way lacks rigidity because the cutting tool isn't supported against the downward cutting force as can be seen in the following photo. (Incidentally, if the compound is adjusted parallel to the ways as is usually shown in ads for little lathes, it frequently interferes with tailstock operations - if it is perpendicular to the ways, it can interfere with cross-slide operation.  Large lathes are unlikely to have these problems of course.)  

  The tool, mounted in the 4-way toolpost, is cantilevered off the compound mounting surface.  When the half-dog screws are tightened to clamp the tool securely, the thinner lower section of the toolholder deflects as a result of the clamping pressure.  The tool is not necessarily tighter and NOW the cutting edge has been forced below the spindle centerline - not helpful if one wants to reduce chatter.




  A couple of decades ago I tired of the chatter when parting off steel workpieces over an inch or so in diameter.  Bad finishes resulted and the parting tool required frequent "touch-ups" at the grinder because of pounding on the tip.  Sometimes the tip would chip and all work came to a halt, occasionally catastrophically (to the workpiece).  Because the parting operation is usually the last (or near to it) a lot of invested time can be lost !

  The following was a quick-fix for the problem and it worked well.  Tapping a hole in the cross-slide allowed installing a 1/2 diameter steel rod directly under the toolpost.  The cutting forces were then transmitted directly to the cross-slide and the carriage.  There was no "rocking" and "tipping" of compound or cross-slide as shown in the simple sketch above.  The capability of the 8 x 18 lathe when working hard-to-machine materials went up by 100%.




  The shortcoming of this "fix" is that movement of the compound is limited, although it's simple enough to unscrew/remove the support rod and restore full compound travel.  With the support removed, rigidity is diminished and chatter returns during heavy cuts using the compound.

  I looked at the Aloris/Dorian-wanna-be's to see if they might be useful for my requirements but decided not.  The tool and tool-holder hang out in space because the size can't be accommodated by the small compound on my machine.  The situation would probably be worse than the original four-way toolpost because of the _greater leverage at the actual point of the cutting tool_.

  Although many people have little use for Armstrong (lantern) toolposts, I used one for years on an Atlas lathe I once owned.  Armstrong toolposts can be very rigid WHEN the forged toolholders - that add cantilevered length - are removed.  Most small Armstrong toolposts are proportioned to hold a 3/8 square HSS cutting tool directly on the rocker.  A configuration like this is one of the more rigid setups possible.  It's clear that there is little cantilevering of the cutting tool once the toolholder has been removed.  It's worth noting, however, that the forged toolholders ARE very handy for many light operations.  (I'm sketching this from memory so the proportions may not be proper.)




  It occurred to me that perhaps a smaller - but more solid - toolholder might be a good idea.  I made this small system - it's nothing like a QC design (and is not very quick to change) but it is _very_ rigid.  The lower block is dimensioned so that the top surface is exactly at the spindle centerline.  Grinding HSS tools without removing material from the upper cutting edge is simple and no tool height adjustment is required - makes the toolholder very sturdy.

  The same applies to parting tools and tools of various cross-section dimensions other than the normal 3/8 HSS or brazed-carbide tooling.  When machining a blank toolholder, all that's required is replicating the tool cross-section dimensions and allowing the tool to stand proud about a few mils to allow for clamping pressure.




  This photo is blurry, the lathe was in operation when I snapped the picture.







  (FWIW, the three holes on the toolholder were intended as angle adjustments for the tool.  A socket head cap screw with head diameter turned smooth, was to register in a similar diameter pocket in the compound surface.  There were to be three of these pockets machined into the compound with slightly different spacing than those in the toolholder.

  By removing the socket head clamping screw and inserting it into a different location in the toolholder, angular adjustment could be varied.  When designing the toolholder, I thought this might be useful but I've never implemented the idea.  I never got around to machining the registration pockets in the compound slide.)

  The little toolholding system works OK on my small Emco lathe; I use it when heavy cutting pressures are expected and frequently when the compound slide is needed.  But the four-way toolpost is usually in the lathe - with the support rod underneath the corner of the toolpost.  It just seems more convenient, LOL.  The four-way can easily support .250 DOC in mild steel with no problem - that's good enough for most HSM applications.

  I'm not completely content with either method - QC toolholders are highly addictive and I've used the Aloris system on large lathes in previous workplaces and, in fact, have one on my Sheldon.  I designed a scaled-down QC system for small lathes although  I doubt that I'll ever make this system - there's just no need for me to produce more than two or three parts at a time.  It was more of a mental exercise, I suppose …

  The point of this post is to suggest that a quick change toolpost, mounted to the type of lathe usually found in the HSM shop, might add convenience but often is less rigid than traditional toolholding methods.  This is a typical QC system on a larger lathe – the overhang from the support of the compound is apparent:





 A simple lantern tool post with a 3/8 HSS cutting tool installed.  This setup will take heavier depth of cuts than a QC tool holder and is more versatile albeit not as convenient.


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## caster (Feb 7, 2015)

Thank you,  this has been a very educational and relevant post.  Now to figure out and build an appliance to replace the compound.

Caster


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## Ulma Doctor (Feb 7, 2015)

i like the idea of the tool support on the cross slide, great idea!!!
:thumbsup2:

thank you for sharing your knowledge and experience with all of us!
mike)


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## bladehunter (Feb 7, 2015)

For a lot of what I do, simple spacers for wheel swaps and other things not requiring a taper I just replaced my compound with a piece of 50x50 BMS and sat the tool post on that. Reduced the chatter a great deal. Oh and this is not something I've seen mentioned, somewhat off track, but on the RH leadscrew bearing\support I used 2 thrust bearings.


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## GarageGuy (Feb 8, 2015)

Parting has always been difficult for me on my well worn 1945 Logan lathe.  The exaggerated geometry you show in your original post is exactly what was happening to me.  I decided to take a different approach.  Sort of the opposite of trying to add rigidity.  

I saw a couple of YouTube videos (one from Tom at Ox Tools, and one from John on his Doubleboost channel) that mentioned a swan neck or spring tool holder.  These aren't new, and Williams and Armstrong made them for lantern style tool posts decades ago.

I decided to try to make one that would fit my AXA QCTP as an experiment.  The spring tool holder backs the cutting tool out of the cut rather than tipping into the cut and making things worse.  My first prototype is big and kludgy, but works like a charm.  I plan to refine it a little, and make it a little smaller.  Here is what I made:




and here is what it looks like in action:

[video=youtube_share;vB-9P8G7n48]http://youtu.be/vB-9P8G7n48[/video]

If you look closely at the video, you can see the tool flexing and backing out of the work, but continuing to cut smoothly.  Before I made this tool holder, I was not able to part steel at all.

GG


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## extropic (Feb 8, 2015)

snip "The little toolholding system works OK on my small Emco lathe; I use it when heavy cutting pressures are expected and frequently when the compound slide is needed.  But the four-way toolpost is usually in the lathe - with the support rod underneath the corner of the toolpost.  It just seems more convenient, LOL.  The four-way can easily support .250 DOC in mild steel with no problem - that's good enough for most HSM applications."


Randy, Thank you for the very well prepared, presented and informative thread.

I think I picked up a significant typo (in red above). You meant .025, didn't you?


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## great white (Feb 8, 2015)

While I could see the "spring holder" working, this video kinda of made the light come on: 

[video=youtube_share;KETVR9qtEmY]http://youtu.be/KETVR9qtEmY[/video]

Thanks for the original posting that brought the spring tooling to my attention. It may be an option if I find I get chatter I can't control when parting on my atlas (still waiting to pick it up).


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## RVJimD (Feb 8, 2015)

I saw the picture of the support post and ran directly to the shop and tried it out!  I measured from the bottom of the tool holder to the cross slide and cut a piece to fit in there.  I left it a bit long, loosened the hold down nut on the tool post and put the rod in place and tightened it back up.  I just wanted to try it before I drilled and taped a hole for a more permanent and adjustable post.

i think it works great, this is at least my third mod to improve ridgity and it is by far the most simple and easiest to implement and remove when not needed!

thanks a bunch for the idea!

jim


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## road (Feb 8, 2015)

A very interesting thread.  I have been working on the issue with my lathe. I use a 4 position post wich I prefer.  I have a QTCP but I dont like it. I have tried a few mods to it but it is still the same issue of the cutting tool hanging out too far off the edge and resulting in the cutter flexing down or as said spring action. I could actually see the compound and carriage flex.    
I work mostly on aluminums. My parting operation is not bad at all. I can get a smooth clean parting finish.
  I do need to fine tune the carriage and compound adjustments.    

As you can see in my photos I like to keep the tooling is close to the stud. Most of the time my compound is set at 25 -35 deg.  Thus keeping the cutter closer to the stud as possible with little overhang. 
I changed my stud to a 3/8 -16 for rigidity as well. 
I also have what I call my single cutter holder. I still need to install a bushing for the stud and make a top clamp block for it.


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## randyc (Feb 8, 2015)

extropic said:


> ....Randy, Thank you for the very well prepared, presented and informative thread.  I think I picked up a significant typo (in red above)... You meant .025, didn't you?



Take a look at thread I posted about making a yo-yo.  At one point in that thread there are photos of the little Emco turning a steel mandrel.  Note the chips coming from the HSS tool


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## randyc (Feb 8, 2015)

GarageGuy said:


> ...I saw a couple of YouTube videos (one from Tom at Ox Tools, and one from John on his Doubleboost channel) that mentioned a swan neck or spring tool holder.  These aren't new, and Williams and Armstrong made them for lantern style tool posts decades ago.



And for those that have never seen one, there are a couple of them in this collection.  Both parting and threading tools are shown in the spring configuration.  Apologies for quality, these came from an old book, Care and Operation Of A Lathe courtesy Sheldon Machine Tool Corporation.


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## randyc (Feb 8, 2015)

road said:


> ...I use a 4 position post wich I prefer.  I have a QTCP but I dont like it. I have tried a few mods to it but it is still the same issue of the cutting tool hanging out too far...



We share the preference for the 4-way tool post.  Most people whine about the lack of height adjustment (for centering the cutter) in these tool holders but it hasn't always been that way.  Take a look at the lathe tool holders in Machinery's Handbook and we'll find that older 4-ways had a rocker in each position for adjustment, just like Armstrong tool holders.

It is possible to improve a QCTP with a simple modification that is much like the post that I added under my 4-way.  The following is a posed photo just to show the concept.  Drilling and tapping the underneath side of a QC tool holder would allow a set-screw to be used for supporting the tool holder.

The adjustment would be somewhat of a trial and error process which could get tiresome.  Also the compound would probably have to be moved to some inconvenient angle so that the set-screw rests solidly on it.


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