# HF mini mill air spring conversion



## RB72 (Mar 1, 2014)

Just completed installing an air spring on my HF mini mill.   I used a method I had seen on a youtube video.   Basically installing the air spring using the existing bolt used for attaching the torsion spring to the head and the left rear mounting bolt used to secure the mill to the bench.    That way the height of the machine was not increased.    I selected a 40 lb air spring after finding out that the kit supplied by thelittlemachineshop was approx. a 36 lb spring but I had seen comments that it did not completely support the head.   I made an adjustable bracket at the top so the spring attachment point could be tweaked in order to get full height extension and be able to get down to the table on the lower end.    I have done some basic testing and it appears to have solved the issue with head drop.     I still need to replace the rack gear bar with the longer 14" one sold by littlemachineshop so the head travel will be able to use all of the column.
I have attached a few pictures.


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## wrmiller (Mar 1, 2014)

Nice install! 

I have the LMS kit on my little mill and it seems to work fine. I do like the extra z-axis travel with the addition of that longer rack.

Bill


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## DennisK (Mar 15, 2014)

I have absolutely no head drop with LMS' air spring kit installed as directed.


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## RB72 (Mar 16, 2014)

The air spring conversion really improves the usabilty of the mill for me.  I can now use the z axis fine adjustment knob without having to put upward pressure on the coarse adjustment handle. Just installed the longer rack. It's nice to be able to clamp my work when needed directly to the table without having to use 1-2-3 blocks etc to raise it up so the mill will reach it.


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## iron man (Mar 16, 2014)

Those are just auto hatch or hood struts they are cheap for cars how much is the kit?


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## darkzero (Mar 16, 2014)

iron man said:


> Those are just auto hatch or hood struts they are cheap for cars how much is the kit?



Yup, look like typical gas shocks. I wonder why they call them air springs or are these different & have an actual spring inside them? I was looking into installing some on my mill. Do they make a great improvement?


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## n3480h (Mar 16, 2014)

Nice install, RB72.  Put the LMS kit on mine last week.  Very happy, no head drop, and more Z travel at bottom and top.

Tom


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## wrmiller (Mar 16, 2014)

Doubt they have an actual spring in them. But on the little bench mill sold by HF/Griz/LMS/MM they really do help make the head movement more repeatable/predictable. When I bought my little LMS mill I was really disappointed with that rack system on the column, but after doing the conversion I was able to make some pretty precise head movements (I used my 3-axis DRO for verification).

Bill


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## RB72 (Mar 16, 2014)

I purchased the air spring from Enco for $8 or $9 bucks.  Bought the ball studs from Autozone for $3 and used some aluminum I had to make the brackets.  The LMS conversion kit is about $40 but it includes the extended z axis.  After I purchased the extended rack from LMS my cost was about the same as the kit from LMS but I did not increase the height of my machine except for about 1 inch so I could get the extra use of the extended rack.


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## rpatton (Apr 4, 2014)

Glad I found this thread, I have seen this conversion in other threads but no explanation as to why you would do it.  Now I know.


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## C-Line (Jun 30, 2014)

Hi-
I'm trying to decide between this approach and the LMS kit since I have limited clearance above the bench where my mill is mounted. For those with the LMS kit installed, how much extra height is required at the top of the mill?
Thanks /James


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## chip maker (Jun 30, 2014)

This is also what I've been wanting to do with my mill but didn't care for the extra height created by the kit from LMS. How long of shock did you use? As you stated it is 40lbs and does that mean you have it compressed when you install it? I also like the upper bracket to alow for extra adjustment. Great setup and Thanks for sharing the info. I know that AutoZone also sells the shocks as well but don't know the cost.  John


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## wrmiller (Jun 30, 2014)

The LMS kit has the longer rack, which gets the head all the way to the top of the column. The spring assy sticks 13 3/8" above the top of the column when the head is all the way to the top.

Bill


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## RB72 (Jul 1, 2014)

The air spring I used was from Enco.  Open it is 17.19 in and compressed 6.18.  It was installed uncompressed.  Using my adjustment bracket the spindle gets within 1 1/2 in. from the table and on the top end within 1/2 in of the top of the column.  Both of those would change with length of adjustment bracket and or length of air spring.  It has been working well for me.


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## C-Line (Jul 2, 2014)

@RB72 and @Bill: thanks for the info.

RB72: It looks like you have iGaging DRO's installed. No interference problems with your air spring mod? Did you have to do anything different with the Z-axis DRO mount to accommodate the air spring location?


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## RB72 (Jul 3, 2014)

I did not remove the old torsion spring so I just needed to make sure there was clearance between it and the scale.   I just left it there as a backup in case the z axis dro went bad so I could continue to work.   I mocked it up before I attached everything to make sure there were no issues.


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## natoround (Jul 1, 2015)

darkzero said:


> Yup, look like typical gas shocks. I wonder why they call them air springs or are these different & have an actual spring inside them? I was looking into installing some on my mill. Do they make a great improvement?


 The name  gas spring is a generic engineering  term. I have  seen them referred to as gas springs when  used to  operate a air rifle. Turns out compressed gas is considered a spring. I can't  really say it  matters  what its called as long as they work.  I think the  first name  we learn  for something seems to be accepted as  correct.


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