# Grizzly G0619 Column Stiffening



## RodSME (Mar 29, 2017)

DAT510 asked if I would post info on my project to stiffen the column of the Grizzly G0619 in torsion.  Here it is.

RodSME


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## DAT510 (Mar 29, 2017)

Great work and analysis!  I'll definitely look at upgrading my mills with your mods. Thanks.


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## hman (Mar 29, 2017)

Nice analysis!  I think I may have something additional to contribute.  I recall learning, many years ago, that a "closed section" is extremely good at resisting torque.  The column of your mill is open at the back, thus not a closed section.  Just for fun, you should try modeling the addition of a more-or-less continuous plate to attached to the back of the column and closing it.  Maybe something like your rear plate, but going all the way to the top of the column.  Shouldn't have to be ½" thick.  ¼" would probably work wonders.

Disclaimer:  I don't have an 0619 myself, and don't know what interferences or complications might crop up if a plate is added to the entire back of the column.  If nothing else, you'd have to modify the arm that holds your DRO read head.  All I can go by is what I see in your Picture 2. 

Since you've added the internal bars, it should be easy to add a full cover (or even a plate to cover above the existing rear plate) by screwing it to the internal bars.  Without them, adding a full cover would require drilling & tapping into the back edges of the casting.  But if you want to model the idea of just adding a full cover without the internal bars, that might be of interest to others who have the same mill.

Hope this helps!


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## Rustrp (Mar 29, 2017)

hman said:


> Maybe something like your rear plate, but going all the way to the top of the column. Shouldn't have to be ½" thick. ¼" would probably work wonders.


Connecting the two sides would improve the strength a lot. It would be beneficial to have the rear plate and anything added be a complete unit, connected by whatever means you may have. If the rear plate and the additional piece are not connected strength will still be gained.

PS. Rod, if I were doing this project from the beginning, I would plan on inserting a channel shape into the back of the column and fastening it in as you have done with the machine screws. The deflection you are getting is in the column above the rear plate you attached.


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## DAT510 (Mar 29, 2017)

The G0619 lifts the head from the back, using a leadscrew inside the column.  This prevents the back from being completely enclosed.


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## Rustrp (Mar 29, 2017)

DAT510 said:


> The G0619 lifts the head from the back, using a leadscrew inside the column.  This prevents the back from being completely enclosed.
> View attachment 230009


So anything flush.....Nah, I see it now, plus I can see  the stiffening ribs cast into the front. This limits the amount that can be done. There is one more option but the effort is limited by the resulting  change so it's best to work it as it is.

Edit: With a plate at the top and a C-shaped long plate connecting the top and bottom plates you might get a little more rigidity. Something 1/2" thick by the width of the column.


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## hman (Mar 29, 2017)

DAT510 said:


> The G0619 lifts the head from the back, using a leadscrew inside the column.  This prevents the back from being completely enclosed.


Aw, shucks!  So much for my brilliant idea.  Sorry, guys.


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## RodSME (Mar 29, 2017)

I didn't want to go into much more detail, but I probably modeled about 8 different ideas to stiffen the column in torsion.  None of them was as good as the way I finally incorporated into the 619.  I modeled adding a back plate to the top of the column above where the wrap around bar for the Z axis nut goes.  It didn't offer any improvement.

As I noted in the analysis, the measured deflection is about 2x the calculated amount.  I guessed that a possible explanation for that is the fact that the model is one piece and the reality is made up of separate pieces.  It's a bit of project to get at the back of the column given how I have the bench setup.  The next time I open the back, I'll consider epoxying the vertical bars to the column.  This should tie them in better.  The only problem will be if the bars extend down too far.  If they block removal of the lower pillow block supporting the Z axis lead screw, I can't permanently attach the bars.  If I have to and it doesn't weaken the assembly, I may be able to take a bit off the bottom of the bars.  I'll also use bigger pins to tie the rear plate to the internal bars.

If I had realized that the mill had this design deficiency, I probably wouldn't have bought it.  I bought it through craigslist, so I got what I thought was a good deal.  I added a DRO and built a bench that's pretty elaborate, so I'm into it for too much to consider switching.  I've learned to "nurse" my  cuts along.  Since I'm retired, I just have to remind myself I have the time to do the job more slowly.


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## majorm (Apr 9, 2017)

Ive been reading allot about epoxy granite over on the CNC zone site and am thinking about giving it a try sometime.  My mental picture is to add some studs in the sides on the column and then use a piece of PVC to create the mold for the Z lead screw and block to move up and down.  The rest would be filled with epoxy granite.  Ill probably do the base at the same time and create a 3 or 4" riser for the column as well.  I have the parts minus the electronics for a cnc conversion so all of this will be done at the same time.  The epoxy granite looks pretty promising for what it is and should add a decent amount of mass and vibration dampening.


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## RodSME (Apr 9, 2017)

In response to majorn regarding using epoxy granite to stiffen the column of the G0619, I'm sure it would do a great job of adding material, thus stiffness to the column casting.  Just a couple of thoughts.  It isn't possible without a major redesign (namely moving the z axis leadscrew to the front of the column) to close in the back of the column completely.  See the photo that DAT510 included in his posting.  Two, the two 3/4 x 2 inch by 24 inch bars add quite a bit of stiffness to the column.  I don't know what the Young's modulus of the epoxy granite is, but steel is 30x10^6 psi, which is pretty stiff.  The majority of the stiffness in my design is developed by closing in as much of the back of the column as possible. hman's post talking about closing in the column is right on the money.  The more the column can be made into a closed cylinder, the stiffer it will be.  Think of the base of a Bridgeport.  Big and sort of conical shape.  Most stiffness for the mass.

Be careful not to lock in the z axis leadscrew and support blocks.  Someday you may have to replace them.


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## Rustrp (Apr 9, 2017)

The amount of rigidity you will achieve is limited by the slot that must remain open for the screw. Making a full connection with reinforcement from the top of the column, then along the sides and connecting to the base is close to as good as it gets.


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## majorm (Apr 9, 2017)

RODSME:  Your comment made me go look up the Youngs Modulus of epoxy granite and lets just say homemade epoxy granite and your right on.  While it does have vibration dampening and weight going for it its not as good as steel for stiffness.  Ill have to keep thinking about this.  There is a person with a cnc conversion that mounted the screw to the outside of the column but this was on a cnc conversion.  There should be a video on youtube about his machine to show how it was done.  It was another guy playing with epoxy granite and he filled the entire column with it so that was the reason.  

Thanks for posting your mod as well.  Its great to see what people come up with to improve these machines.


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## Sloth2009 (Apr 28, 2017)

Random idea.  Has anyone ever tried bolting a heavy frame onto the back of the column and the mounting it directly to the wall?   Something that looked like a vertical bridge with 2 beams and support triangles between them.  This would keep the top of the column from being unsupported It would be ugly but perhaps solve the rigidity issue. Even a cable anchor would help keep the column from flexing forward.


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## RodSME (Aug 17, 2017)

In my March 29th post, I mentioned that the FEA torsional stiffness of the column was twice the value I got when I measured the mill after modifying it.  I attributed that to the fact that the two side plates were bolted to the inside of the column and not one piece as in the model.  I mentioned that I would consider epoxying the bars to the inside of the column if I had to access the area in the future.  Well, the future is here.  I epoxied the bars and increased the size of the pins attaching the back plate.  The results were impressive.  The column is now 4 times stiffer in torsion then the original modification.  I was curious about the stiffness of the head stock in the X direction and so I performed a similar measurement to see what the stiffness is.  Low and behold, the head stock is now more flexible than the column.  I have been away for awhile and as such haven't tried the mill with the mods.  I'll post my thoughts on how much, if any the mill has been improved when I actually use it.

I've attached a .pdf of the updated report I wrote.  The update discusses the recent mods.


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## Sloth2009 (Aug 19, 2017)

RodSME said:


> In my March 29th post, I mentioned that the FEA torsional stiffness of the column was twice the value I got when I measured the mill after modifying it.  I attributed that to the fact that the two side plates were bolted to the inside of the column and not one piece as in the model.  I mentioned that I would consider epoxying the bars to the inside of the column if I had to access the area in the future.  Well, the future is here.  I epoxied the bars and increased the size of the pins attaching the back plate.  The results were impressive.  The column is now 4 times stiffer in torsion then the original modification.  I was curious about the stiffness of the head stock in the X direction and so I performed a similar measurement to see what the stiffness is.  Low and behold, the head stock is now more flexible than the column.  I have been away for awhile and as such haven't tried the mill with the mods.  I'll post my thoughts on how much, if any the mill has been improved when I actually use it.
> 
> I've attached a .pdf of the updated report I wrote.  The update discusses the recent mods.


Are there any pics you can post of how you achieved this?  For some reason I am unable to view the attachment.  Will have to try later on a different device.


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## RodSME (Aug 20, 2017)

Sloth2009 said:


> Are there any pics you can post of how you achieved this?  For some reason I am unable to view the attachment.  Will have to try later on a different device.


If you are unable to open the attachment, I can e-mail you a copy.  Reply to this post.


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## Sloth2009 (Aug 23, 2017)

RodSME said:


> If you are unable to open the attachment, I can e-mail you a copy.  Reply to this post.


Very nice write up!


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