[CL_MotoTech]

Really nice work! I look forward to your progress.

[peteeng]

Hi Switch - so why are so many companies making machines from UHPC? Granite is 70-89% quartz with some alumina so should be stiffer then 100% quartz (its red because of some iron in it ). The gain in stiffness by increasing the steel thickness for the same cost of the epoxy granite is a much better strategy then using the EG but you are now committed to your steel size. I buy plywood that is stiffer then 14GPa (F27 is 18.5GPa)... I agree about the rust I have samples here that have steel fibres with rust. The proof will be in the pudding, I'm sure your machine will be a good one... Peter

[mactec54]

But-back to the primary concern, static stiffness. I want to make the stiffest machine I can afford to build, as I will be using it for both steel and aluminum work. I am targeting a Haas-style "Office Mill", as they use the same size linear rail hardware that I already have, and I think that the stiffness of the linear rails/guides is going to be the limiting factor-as the 25mm rails only use M5 bolts to attach to the column, so the limiting factor for stiffness is going to be the M5 mounting hardware.

So, the machine structure needs to be limited by the M5 bolts holding the rails on.

I think you made a mistake with the Capscrew size 25mm linear rails use's a M6 every 60mm is more than enough to hold the rails in place, you will have a loading spread over the 2 Bearings on each side

[llilrex]

looks pretty nice. are you expecting 1000lbs of torque on the column? I am just wondering what type of machine you are going for. high HP low torque or High torque low HP. looking at the ratios of the column and cartridge holder it looks like you could get 8 to 9 microns with at 1000lbs cut force. that's pretty good. using cutting data from kennametal that could be a .75" HARVII 3 running at 2200 RPM using about 8.7 HP with a MMR of about 3cu in/min ,1" LOC, .04" DOC side cutting with 43HRC steel work and a torque of about 20ft/lbs. with a deflection of about .0005" assuming a 1'6" center of column and center of spindle which will give you that 1000ft/lbs of torque on the column when cutting on the X axis (there abouts). I am not sure that the column can actually behave this way being only 6X10 inches. I would check my simulations for sanity. I think I would mock up the table and spindle, fix it to the column and run the simulation just to make sure it reflect a cutting scenario. using the 100 to 150N /.001 mm mentioned by peeteng might be a good thing to do too. I am not sure where peeteng got that number but it sounds reasonable to me (edit: I know where peeteng got that number I was being dumb and didn't recognize it at first, it is a good comparison standard to go by).

[switch2472]

Lilrex,

I expect about 400lbs of torque on the column. With a 2.5HP spindle motor, the spindle limits the forces here. I computed the loads based on a .5" 4-flute Harvey Tool end mill running 1900RPM, cutting a 0.400" deep slot in one pass at 10IPM as my maximum spindle load, with material as RC35 4340 steel. This is a slightly more than 2.5HP cut, according to Harvey Tool, and I've made this cut before at my old job on a 2.5HP Bridgeport clone.

The reason for a 2.5 to 3HP spindle is that it's a 30 taper machine. Other than a face mill, the tool holder isn't ideal for holding shanks larger than 0.5" and it's very easy to overpower the taper if you put 10HP of spindle drive on a little 30 taper.

As to realism...I bolted a torque arm to the linear rail stands this afternoon, and drilled four out of the 8 mounting bolts into the concrete floor of the shop. Bolted the column to the concrete floor, and put a torque wrench on the 16" arm. Pulled the torque wrench to what would be 400ft-lb after adding the length of the torque arm to the wrench, and attempted to measure deflection in the column.

Pull #1 moved the column 0.0071"
Pull #2 moved the column 0.004"
Pull #3 moved the column 0.0061"

And this is with no filler in the column, no internal ribs (which are in the modeled column, they just haven't gotten here from the laser cutter yet) and no top plate welded in (the top of the tube is still open).

100N is only 22lb-f and some change. Not much force, but then 0.001mm is only 0.0000394 inches. I can't apply that little force and measure it reliably with my tools here. Honestly, 100N is not even enough force to fully unload the ballscrew, when you take into account the weight of the spindle carrier.

[llilrex]

those physical tests are what I would expect to see, I must have interpreted your FEA wrong. the 100N thing is a normalized test. if I were to apply it to your tests it would be something like:

assuming .006" at 400lbs at the column,
and assuming 7 inches from centroid of the column to where you measured
further assuming the 16" was standoff from centroid of 5" and 16" represents the spindle center

21/7 = 3
3* .006 = .018" total deflection at the spindle with 400lbs of force which is 1779N at 457 microns
1779/457 = 3.893N/.001 mm

I made a bunch of assumptions about your setup that are clearly wrong but the method should be sound. this calculation assumes that the force loop is going through the floor and then your column and the spindle is mounted where ever you put your arm. it also assumes some things about the centroid of forces on the column and how far your spindle actually is from the centroid. but this is what we mean by 100N/.001mm

obviously you want more then 3.893N/.001 and I think by tightening up the simulation and test you can get to a better representation. as well as with the filler.

the reason why I said what I was seeing might not be right earlier is that the above calculation would have come up to 3000N/.0127 which is normalized to 236N/.001mm and no matter how I looked at it there is no way that the way you did the FEA, it would come up to that, when modeling just the column. so I am glad you did the sanity check. when your machine is assembled I think you can get much higher numbers in terms of N/.001mm I don't think it will be as high as 236N/.001 it depends on the spindle centroid to center and how short the column loop is. I hope that clears up the 100N/.001mm thing.

[peteeng]

Hi Switch the static stiffness of a machine is measured as a spring rate. 100N per 0.001mm tool deflection is a very stiff machine. I've published machine stiffness data elsewhere. . As you describe here you need to convert your numbers to a load/deflection that represents the tool to bed stiffness as a spring rate. Then your numbers can be compared to other machines. You can do this via FE or a real test as you have done. Cheers Peter

100N/0.001mm is 571,000 Lbf/inch stiffness at the tool or 571Lbf/ thou

[switch2472]

AH-HA!

I've been reading the 100N/0.001mm as a deflection of the *column* not at the tool. Considerable difference there.

Yes, the internal braces for the column are steel "doughnuts", rectangular rings that are the correct dimension to fit snugly between the two wide faces of the column, but are slightly too long to fit between the two narrow faces-thus they stack into the column in a zig-zag fashion, creating a series of triangular boxes inside the column. These can be rather easily welded in place even after the column is attached to the base plate, as it is.

These doughnuts will provide the equal of a 2"/50mm tall rib, 0.375/9.5mm thick, on all four interior faces of the column. The center of the doughnut is left clear so a solid filling of epoxy-granite can still be installed, and to release air from the "peaks" of the triangle a U-shaped notch is cut out on the short-wall side.

These internal ribs plus the fill are in the simulations, but not in the "bolt it to the floor" test I did.

[peteeng]

Hi All - Germans are so thorough. Peter

https://www.sciencedirect.com/scienc...07850615001444

[mactec54]

The reason for a 2.5 to 3HP spindle is that it's a 30 taper machine. Other than a face mill, the tool holder isn't ideal for holding shanks larger than 0.5" and it's very easy to overpower the taper if you put 10HP of spindle drive on a little 30 taper.

I don't think you would have to worry about the 30 Taper spindle part if built correct, it can use a much larger size than .5 cutter, Here is a CNC Bridgeport I converted to a Horizontal it is vertical as well, I made Built a 40 Taper spindle for it as well but I doubt that I will use it on this machine it has a 6Hp motor driving this 30 Taper spindle and could take more Hp if I needed it, I mostly use this for machining steel plates drilling and rigid tapping it can run a 6" face mill for face milling of 5" and 6" steel plates, so don't think the 30Taper is the weak point in your build 5Hp and more would not be a problem if you had a need for it

[switch2472]

Still having issues getting the simulation to work out properly.

Found out that my sims aren't accounting for any kind of internal structure in the column-any bracing I install is meshed but isn't loaded when the column is. If I put in the full epoxy block model it *does* get loaded, but trying to fit in and get the welded-in bracing to simulate, it just doesn't load the brace and the braces "clip through" the outer tube, and the color map shows zero loading or deflection.

Anyone out there hot stuff at Solidworks Simulation and able to give me some tips on how to get this model to simulate in a realistic manner?

[peteeng]

Hi Switch - I've not used SW but with this sort of mesher the faying surfaces have to be perfect for the mesher to making a contiguous mesh. Can you export a step file so I can look at it? or some screen shots of the model? have you created the epoxy bits by booleaning the steel bits out? Plus the bracing is this an edge to a surface? The mesher won't mesh across an edge I think. Boolean is a solids addition or subtraction. The epoxy bits have to be exact internal parts to the steel parts... If you have a body within a body the mesher will ignore one or mesh both as seperate bodies. Cheers Peter

[switch2472]

In SW when you create the mesh, you select faces that are bonded and assign them a rigid bond or a flexible bond, if flexible you have to designate a LOT of other information so I have every interface assigned a rigid bond.

At least I thought I did, I'll spend more time on it tonight.

[switch2472]

New thoughts.

I've been given a cast iron column from a Hardinge-Handsvelt sinker EDM. It's 39" from base to the top of the casting, and 10.5" x 8.5" across the column. It does have a big cast in L-shape that is nicely ground cast iron on the top. The column wall thickness is about 1/2"-13mm, and the corners are increased to about double that thickness. It does have some internal ribs but it's mostly hollow.



https://imgur.com/yGcqM1C

It's the same size as the welded steel column. I'd have to do exactly the same machining to it to mount the rails, and I'd have to mount the rails or the blocks on huge risers to fit the ballscrew in between them. It would scrape in much faster than the welded steel, though.

The question is, Is it going to be more advantageous to use my welded steel column, with it's slightly less than double Young's modulus, or the cast iron pillar? (Steel at 200GPa, vs cast iron at 124GPa). My welded column weighs almost the same, and yet I still need to weld in the top cap and internal brace in the welded column.

Basically, all I can see the iron casting having over the steel weldment is 10 times better damping, and 3" more height.

[peteeng]

Hi Switch - Cast iron is not 10x damper then steel. It is clearly damper but it depends on the test method to the degree of how damp it is. But dampness is a plus and its really up to you? Are you leaning to CI? Peter

[switch2472]

I still think the welded steel column will be stronger and stiffer in the end. The cast iron pillar was just given to me.

I will eventually do something with it. Also there are cast iron 3" wall thickness machined tombstones available local that are 39" tall and 12"x12" with a 14"x14" base on them, they would be considerably better, however I'd have to do a LOT of machining on one face to get room in there to fit the ballscrew.

I've dug up some 4" OD steel pipe, but it's not big enough to fill the center of the column. I am currently hunting some 5.25" OD, 0.5" wall thickness pipe. None is in stock locally.

According to my last few design-simulation cycles, placing the .5" thick wall pipe down the center, and filling the void on either side of it (It will contact the front and back faces of the column) seems to up both the torsional stiffness and the damping. Still well short of the 100N/1 micron goal, though.

[peteeng]

Hi Switch - Strength is rarely an issue in machine design. To achieve a 100N/0.001mm stiffness machine means tonnes of metal. Will be interesting to measure your actual stiffness when your done... How are you estimating damping via simulation? and what fill are you using? Peter

[mactec54]

I still think the welded steel column will be stronger and stiffer in the end. The cast iron pillar was just given to me.

I will eventually do something with it. Also there are cast iron 3" wall thickness machined tombstones available local that are 39" tall and 12"x12" with a 14"x14" base on them, they would be considerably better, however I'd have to do a LOT of machining on one face to get room in there to fit the ballscrew.

I've dug up some 4" OD steel pipe, but it's not big enough to fill the center of the column. I am currently hunting some 5.25" OD, 0.5" wall thickness pipe. None is in stock locally.

According to my last few design-simulation cycles, placing the .5" thick wall pipe down the center, and filling the void on either side of it (It will contact the front and back faces of the column) seems to up both the torsional stiffness and the damping. Still well short of the 100N/1 micron goal, though.

You should be able to find some hydraulic tubing that size

[switch2472]

It is a standard size, however nobody local has any to sell me right now. I can order it in...at an obscene cost.

I'm looking at how to hang the counterweight on the Z-axis too, either I need to buy an air spring or a bit of linear rail. I think the air spring may be cheaper, but has one major downside. If the air spring fails, the head falls. The counterweight just has to exist and it works.

[mactec54]

It is a standard size, however nobody local has any to sell me right now. I can order it in...at an obscene cost.

Hydraulic tubing is always expensive, if you can find it unmachined it can be much cheaper

I'm looking at how to hang the counterweight on the Z-axis too, either I need to buy an air spring or a bit of linear rail. I think the air spring may be cheaper, but has one major downside. If the air spring fails, the head falls. The counterweight just has to exist and it works.

You could make the tube in your column, into an air cylinder a lot are using a simple air cylinder for doing this or air over oil cylinder, counter weight style can also use an air cylinder