[sensph]

How would you modify an IH type mill specifically to improve rigidity. I don't mean dampening. I mean how would you modify the column and base to reduce the deflection of a few thou when hand pressure applied? I'm sure you could live with this deflection but if you were to approach adding aftermarket rigidity to the mill what might be an effective way?

Steel ribbing inside the column and base ? or ...

ideas?

Best Regards,

Simon

[Runner4404spd]

make the column thicker with a concrete or composite wrap. although i think the deflection your seeing may be a problem with the dovetails and not having the gibb tight enough.

[InspirationTool]

I second the "check your gibs" suggestion.

-Jeff

[sensph]

All,

Many thanks for the replies.

I should have said that this deflection is measured from the ways of the vertical column ( ie no spindle or vertical slide mounted ) to the table with both the x&y locked. By pushing on the mill column i can note significant deflection of 2-3 thou either way by reasonable pushing and up to 4-5 thou with enough strength to tip the mill a few inches off the floor which is attached to a very heavy cast iron stand.

The mounting nuts for the column are as tight as they can go. The base of the column and top of the column mount i think are square. This is because when I had it mounted up i measured around 0.001 ~0.002 deviation on x over entire table. same on Y. pretty much full travel all ways around seemed to be 0.001 to 0.002.

But the deflection is making me scratch my head. The only thing I could think of was that the thickness of the coumn cast iron and base cast iron would just give this deflection. ie the machine is what is is.

I must point out that this is a IH type and hence may not have any addionatl ribbing in base that i seemed to think the IH ones had.

So given above I was wondering how you might work out this problem. I know that you could live with it. But I was wondering if it could be resolved somehow?

TIA

Simon

[Runner4404spd]

if your cncing it then take a half round tube and place in the center of the column where the screw goes. then take and fill the rest of the column with concrete or epoxy granite mixture to stiffen. the other option like i stated above is to laminate layers of material to the outside of the column making it more robust. although i really do still doubt the actual column is deflecting. i think its more along the lines of it not being bolted down square or an issue with the indicator or setup.

i don't know how your measuring this but i have a hard time believing at the bottom end of the column you'd be getting that much deflection.

[philbur]

Fabricate a massive steel base and column, with lots of internal ribbing. Place the mill on the fabricated base and bolt the mill to both the fabricated base and column, with shims as appropriate. Fill the fabricate column and base with sand for additional dampening performance.

Regards
Phil

How would you modify an IH type mill specifically to improve rigidity. I don't mean dampening. I mean how would you modify the column and base to reduce the deflection of a few thou when hand pressure applied? I'm sure you could live with this deflection but if you were to approach adding aftermarket rigidity to the mill what might be an effective way?

Steel ribbing inside the column and base ? or ...

ideas?

Best Regards,

Simon

[mracer3]

What brand and what size is the mill.

[ozzie34231]

Anchor the top of the column to a concrete wall or concrete block wall.
If the mill is to experience wide temperature swings the problem gets tougher.

Ozzie

[sensph]

The mill is like this one. http://www.chesteruk.net/store/super_lux_mill.htm. It probably an older model though. Also mine has a cast iron stand not the steel one shown.

I can understand the reluctance to beleieve the amount of deflection. I was surprised. Im sure the indicator setup is ok. The indicator is good and I can, and have repeated the readings with another one. I had the indicator mounted in a mag stand on the table. I then wound the Y towards the ways until the indicator was about mid travel.Again to the actual colum ways not to the Z head mount. X and Y locked by tightening the gib screws and then pushed on the top of the column. Voila deflection.

2-3 thou under moderate pressure, 4-5 under enough pressure to tilt the mill.

Measured at the height of a mag stand above the machine table. So only about what 6-7 inches up the column.

I cant stand behind the fact the column base mount is OK so well.

All i can say is that it was good, because when mill measured with head on and indicator in locked down spindle I got 1-2 thou consistency all ways around. I know the bolts are as tight as they were.

I have mounted the head and measured a few times and got 1-2 with and indicator over the length of travel but still this 2-3 deflection under fairly light pressure and 4-5 with a good shove. I've been around this loop a few times now.

How would you go about ensuring the column to base was a good mate etc?

I wouldn't mind removing this doubt before constructing a big base or filling up the column. Although I can see both these routes as options.

Anyone had this sort of problem before becasue of the base or another reason?

Thanks for all posts so far. Keep them coming.

I'd like to find out where and why im seeing this deflection and how to remedy.

Best Regards,

Simon

[tai42]

This might be a pain to set up, (and I'd have to do the math to see what kind of precision you would need on the indicator), but one possible diagnostic is this.
1. Rig up a system to apply the same amount of force to the same place on the column for multiple measurements. You may be able to do this by hand repeatable enough, but something involving a rope connected to the top going through a pulley with a weight on the end would be better.
2. Measure the indicated deflection at several places up the column.
3. See if the deflection is linear, or has a curve to it.

A linear deflection would suggest that the column is tilting in a ridged fashion, and the problem would have to do with the interface between the column and the base. (Weak bolts, larger washers, maybe need to grind flat the interfacing surfaces, etc.)

A "curved" higher order deflection would suggest the base is fixed and the column is flexing. Then you look at ways to make the column more ridged by filling it with concrete, etc.

Again, not entirely sure this would work without running some numbers and making a model. (I'm an optical engineer, so I tend to be a little anal about such things.) However, there was a time when I would just try it and see what happens. I do think it's important to separate out the problem (flex versus base mounting) as the solution to one may not help the other.

[tai42]

Something occurred to me that might be easier. Put an indicator on the front and back of the flange where the column mounts to the base and see if there is any deflection up and down. (You need to do both front and back since you don't know where the pivot point may be.) If you don't see any deflection up and down, then you're probably looking at column flex. If you do, then your column is pivoting on the base. You should even be able to figure out the pivot point from the amount of deflection and the geometry, which would tell you where the high spot is. This of course wouldn't rule out a problem in the interface from the column to the flange (like a hairline crack, which would be picked up by my previous method) but it may be a quicker setup to try.

[davo727]

Here are some things I did to my rf45 clone mill to strengthen the base http://www.cnczone.com/forums/showthread.php?t=35630 The third post down shows the epoxy concrete fill in my base. Im going to fill the bottom 6 inches or so of the column with epoxy concrete after I see how much clearance I need for my ballscrew in the cnc conversion. Also a 1.25 inch stud through the center. I bet yours is flexing the base where the column mounts to it. Dave

[Cruiser]

No matter what ya do your gonna have deflection, cast iron has a certain amount of plasticity as does anything..... how can a few thou hurt ya. look at what the mill is capaple of. there are some things that are practicle to assist in rigidity where it is needed, but concider it can rip a half inch end mill a quarter inch deep with some respectable authority ! then finish with quite respectable tollerances ! you just fishing with no bait is all !

[sensph]

i am going to try a bit more measurement as tai suggests. a good idea and hopefully reasonably easy to determine where the problem lies. many thanks. i'd never have thought of that.

then depending on what that tells me I will think about what to do next. Davo and everyone thankyou for the suggestions to maybe remedy the flex.

cruiser, yep you may well be right - the machine is what it is. But ithink i'm just one of those who will try the more interseting modifications to eek out a bit more than should be expected from the mill! its half the fun for me. crazy i know. but mad dogs and englishmen

it'll probably be the weekend before i get down the workshop again. I'll let you know what i find.


Best Regards,

Simon

[bohica]

I found Simon's post interesting, although I agreed with the replies to check the gibs.

Since I am in the process of completing a IH CNC mill I thought I would test my mill for the problem he described. I should note that the 4 z column bolts are torqued to 150 ftlbs and have lock washers and these rest on bare metal. I chucked a dial indicator in the head and pushed on the z column about 12" from the top. I was quite suprised that I could get up to .003 change on the indicator, depending on how hard I pushed, but it wasn't really that hard. I would guess about 30-40 lbs.

Now I'm not superman like Simon and did not push hard enough to lift the back end. It's kinda hard to measure how much force that I applied to the mill. So I placed a 20 lb. bar of steel on the head and got .001 change on the indicator. This could be gibs, but I think the square z column is indeed flexing.

Gonna have to think about this..........

[bohica]

Just out of curiousity, I looked up the modulus of elasticity for cast iron. At 70 degrees F, cast iron is 13.4 vs steel at 29-31. Cast iron is quite flexible compared to steel.

[philbur]

I think the figures being achieved are about par for the coourse.

Also concrete and grouts are even more flexible than cast iron (like 3 times) with an index of only 4.5. So filling the column will give only a relatively small percentage improvement in stiffness. Increased stiffness comes from an increase in dimensions so if you really want an improvement you need to add external reinforcement. Its an engineering fact of life.

Regards
Phil

PS: If you are going to spend time and effort to improve the stiffness then spend it where it will be most effective. Fiddling around inside the column is not the solution. Even a solid cast iron column would only be something in the region of 50% stiffer than the standard hollow design. A concrete filled column will be only 20% stiffer. Well designed external support can easily achieve improvements of 400% or more.

Just out of curiousity, I looked up the modulus of elasticity for cast iron. At 70 degrees F, cast iron is 13.4 vs steel at 29-31. Cast iron is quite flexible compared to steel.

[QSIMDO]

"Well designed external support can easily achieve improvements of 400% or more."

Most definitely, and one would not have to be overly engineered to work either.

A section of 3-4" H or I beam sistered to the back of the base up to the top of the column.
Two holes drilled & tapped in the base, two in the middle of the column and two at the top, dimensioned so they fall in the meat of the flange of the beam where you would drill six corresponding holes.

Bolts inserted through the holes in the beam. Once the bolts are through the beam thread two nuts on mid way down the bolts.

Thread the bolts into the base & column and run a nut down the bolts to the base & column, snugging up tightly.
Run the remaining nuts up tight to the beam and there's your strongback.

The bolts and nuts are positioned to tighten against the mill and the strongback independantly so as not to introduce any curvature.
Conversely, one could tighten bolts and nuts as needed to straighten things out as well.

[tai42]

This is the kind of thing that just begs to have a nice FEM model made with various techniques and designs. I might have to give it a go when I have time between projects.

[sensph]

well managed to do a bit of measuring.....

These aren't majorly scientific but i used one arm to push and pull the column as hard as i could and measured the deflection at various points up the column. eache measurement was taken concurently because i had to move the mag stand and hold it in avice etc to get the height changes. as before the deflections were measured with the dti lever on the z ways with z &y firlmly locked down. (in essence no z gibs involved and x & y locked up so no significant gib wobble affecting results). here is what i saw. my dti reads in 0.01mm steps.

height from base of column , deflection when pulling towards me , deflection when pushing away.

5" 0.025mm 0.02mm (under a thou)
9" 0.03mm 0.03mm (just over a thou)
13.5" 0.05mm 0.05mm (two thou)
17.5" 0.07mm 0.08mm (around 3 thou)

No i cant quite figure out if this means my column is deflecting or the base is??? anyone's opinion here welcome.

I guess what I am trying to figure out is if I dont want to live within the remit of the machines abilities where would I make my effort to strengthen it. Steel backbone on the outside rear of the column and bolted to the base? Steel ribbing in the base?


As before I except this deflection performance is normal for this sort of mill? But if you wanted to have a go where and how would you place your extra metal?

If you did want to strengthen what material would you use , steel - what shape thickenss, where? how would you attach - bolts M6, M8, bigger?

Sorry for lots of questions but just running it around in my head

Thanks for the replies so far all.

Best Regards,

Simon

oh forget who said it but superman never been called that before! well i weigh 205 pounds and I bench press around 210lbs on a good day. maybe i can save some money at the gym and just use the column?:idea: