[NewHobby]

Yes of course, great point. I was wondering if there was not some glaring reason not to do it. I don't see it, I don't hear it. Doing it and measuring it is the true test.

[jdrew1]

I'll second that. The part couldn't be much simpler to make. Looking forward to test results.

[handlewanker]

Hi, I quite agree......if you never never go you'll never never know etc.

The other possibility that might occur is by some magical wave of the wand, the vibration has now stopped.......until you use a different cutter with a different number of teeth and a different speed.....that is the effect of a resonant frequency symptom, and it can occur at any point.

Altering the length of the column has changed the frequency at which it will resonate with the cutter rpm and feed rate.

Some people fill the void in the column with an epoxy resin granite mix to do just that.

If the column deflects under load, that is not a problem as it is probably the roughing cuts that move it,and with a much lighter finishing cut the deflection ceases to exist.

What is a problem is column vibration or the rapid movement as the column comes into tune with whatever is affecting it.
Ian.

[migrusch]

You bring up a good point Handlewanker, and I've been thinking about this all day now. (the joys of unemployment)

It's been a couple of years since machine design class, but the way I understand it is that since the bolts are preloaded they only "see" a portion of the load applied to the joint. The rest of the load goes to deforming the remaining materials in the joint.

Anyway, I ran a quick FEA in Solidworks to satisfy my curiosity. Two cases: one plain column bolted to a plate. One column bolted through a spacer to the plate (threads not engaged in spacer of course), with the column shortened by the height of the spacer. Identical loads (100lbf) and fixtures. Bolts were simulated in SW, and I believe SW Simulation models them as elastic since it asks for the Young's Modulus. The deflection results are surprising. For those not versed in FEA, the deflection at the tip of the unspaced column is 0.46mm. The deflection at the tip of the spaced column (at the same 12" distance from the table) is 0.19mm. I can't find any mistakes in my setup but I haven't used SW Simulation that many times. It's very possible I'm missing some crucial detail, but there you have it.

Attachment 213984

Well this is one of the best examples of misuse of FEA I have seen. This is like proving the earth is round......

Surely the whole point of the spacer block is to raise the Z axis. Then why would you apply the force at the same point in both scenarios?
If the operator only needed 12" travel, they wouldn't need the spacer block.

This is no way a problem needing FEA is total overkill for this type of problem, all be it pretty and 'impressive' to some. The is just simple canterlever beam deflection that would easily be calculated (within reasonable accuracy) on a napkin. Anyhow, it's really only the difference between the designs which are of interest, not the absolute value.

Also, of interest, there were comments earlier regarding the thickness of the column walls. Increases in thickness have a poor influance on stiffness, when compared with increasing the overall cross section. Look at the equation for 'second moment of area' which explains the structures stiffness in bending. The depth (in the bending plane) is increases the stifiness with a 3rd power, so clearly stiffness is better achieved by making a 'larger' column, not a thickener one. Having said this, I think the thickness will have more impact on damping vibration, with is equally an issue with milling machines.

[jdrew1]

Wow, sorry to have wasted only my time and effort and no one else's.

The point for those that might have missed it was that with a spacer, the column would in fact be stiffer at the same height, such that the spacer would not negatively affect normal milling operations. Point proven, case closed.

The beam deflection is indeed simple. The bolt and flange calculations are more involved however, and I didn't have a big enough napkin.

[migrusch]

Not having a go. Sorry if it came across like that. I just don't think the evaluation of the design is that complex.

Sent from my GT-I9100T using Tapatalk

[handlewanker]

Hi, you can gain a bit of height by removing the rotating base from the vice too, but that only applies to jobs mounted in a vice.

One day someone will sell steel sub bases with steel back up columns to attach to the back of these mills to make the cross sectional area that much bigger.
Ian.

[109jb]

Well this is one of the best examples of misuse of FEA I have seen. This is like proving the earth is round......

Surely the whole point of the spacer block is to raise the Z axis. Then why would you apply the force at the same point in both scenarios?
If the operator only needed 12" travel, they wouldn't need the spacer block....

I can certainly envision times when the added travel would be beneficial without having to raise the point where the actual machining forces are applied. Like simply changing tools. Say you want to switch from an R8 end mill holder and put in an R8 boring head with a boring bar attached. An R8 tool goes up in the spindle 4 inches, so there can be cases when just a couple inches more or less means the difference between getting the tool out or not. Also, on machines like this, the spindle nose can touch the table, effectively meaning you can use a zero length tool. Being able to put the spindle on the table is totally useless, so why not raise it up and at the same time gain some stiffness at the height where the machining takes place.

As for jdrew using FEA being a misuse, I totally disagree. Yes you can do cantilever beam calculations and get the deflections very close. So go ahead and pull out Roark's and go wild. Present your calculations that most here won't understand anyway. Do it for the beam presented which with the spacer is a cantilever beam of varying cross section, solid for the first couple inches then a elastic bolted connection and then a different cross section altogether. This is not just a trivial constant cross section box beam with a single point load. Also, the graphical output of FEA has the ability to give the layperson an understanding that Sigma = P*l^3/3*E*I can't. Don't forget that Jdrew can quickly put a load case into his FEA that puts a bending load and a torsion load on the column like the machine sees when milling. He can input many load cases to simulate many different machining loads. The FEA used in this case was within Solidworks which I regard as a conceptual design type FEA. Well, what did he use it for graphical depiction of a conceptual design modification to a X2 mill. A true misuse of FEA is not using it where it is overkill, but using it improperly in a way that will yield the wrong results, such as using a linear elastic approach on a non-linear problem. Just because a problem is simple enough that a hand calculation could be done doesn't mean that an FEA is a misuse. I can pound a nail in with a hammer, so is using a pneumatic nail gun a misuse of that tool?

Also, in regard to section thickness not having as profound an impact on stiffness when compared to the overall cross section, I agree that overall cross section will have more impact, but here we are talking about a machine that is already designed. Simply putting a a larger overall cross section has ramifications that thickening the walls does not. Like how the column mounts to the base. With larger dimensions you will likely have to redesign the mounting bolt pattern, and then maybe the base, and then .... Simply doubling wall thickness, although it won't provide as much of a stiffness increase, it will provide some stiffness increase, and it won't have the possible impacts that increasing overall section can have.

[NewHobby]

OK so I don't ant more Z so I can Fly cut or even mill at the top of the column. I want it so I can "occasionally" raise it to drill a hole, drill bits and chucks take like 6" of the travel, turn a part on it's end and all of a sudden you need a WHOLE different mill just to drill? I don't think so. Just need to increase height for drilling now and again. Actual milling will be below the stock column height and as a benefit during normal use, say right above the vise, the column would indeed be stiffer as it is actually lower on the column.

Like 109jb pointed out, changing tools and lots of thing NOT involving cutting make increased Z height useful and you can do it without compromising normal height milling rigidity.

handlewanker, I wondered the same thing, I suspect cost would be the issue. But making such a thing for individual use is a different story. Surprised I have not seen it yet myself actually.

I have an idea for a brace as well. Will likely fill the column and base with epoxy and heavy sand mix.

[migrusch]

Ok, So I may have been heading towards flaming there..... sorry. Having a bad day at work and probably shouldn't be venting on a forum.

I still think the better comparison is the deflection at the top of the new travel vs the current 12".
I don't hate FEA or anything like that, but in the wrong hands it can be misleading. I feel that for simple problems (or problems that can be reduced to a simple problem) it is important to understand the mechanisms that impact the outcome.

So I see what 109jb is saying, but I don't belive that anyone needs extensive knowldege, a degree or Roaks reference to gain an understanding of the mechanisms at play. Certainly if this is beyond their understanding, the can't be expected to use FEA correctly.

What I am trying to say is that if the basic principals are shared and put into the context of these machines, this is more beneficial to everyone on the forum than FEA images.

Regarding wall thickness. I am not advocating increasing the size of the column, we have to work with what is comercialy available to suit. I am trying share some information so that everyone is clear on what is \ isn't important and to what extent so that when comparing machines \ designs we are not misled to think something will have a biger influance than it actualy might.

[NewHobby]

Ok yes, makes sense and appreciate the input for sure!

[jdrew1]

It happens migrusch, no hurt feelings.

Let's get back to building machines, yes?

[wizard]

Handlewankers points are technically correct but are really of no value in this situation.

Let's look at it this way, engineers have been modifying machine tools for years to address a specific requirement. In doing so they realize that the alter the mechanics of the machine which may require adjustments in the way the machine can be used. It really is no big deal.

You want to add a riser block which obviously will increase the lever arm that can act on the base casting. That could be a huge problem or no problem at all depending upon how you use the machine. If you extend the column all the way up it may force you to limit your drilling capacity, but let's be honest that is already limited on these machines.

That is exactly how I see it, at 2 inches above the part I am not 2 inches lower on the column than normal where is is stiffer.

I doubt very much that you will see much difference at all in stiffness at the lower positions. Effectively the lever arm will impact things higher above the table and having doubled the bolted connections probably won't help you much either.

I tis is ince in a while frilling somethiente that does not fit. Any of these bench top mills suck cutting at the top of the Z,

If you already understand this then you are going into this with open eyes. As such it is worth the time to experiment with the idea.

the spacer is not trying to fix that, itis ,aking it so I can turn a part on the side and drill it once on a bluie moon. Until then it "should" be stonger over all a normal operating ranges in my thought as well.

I'm not sure I buy the stronger idea. On the other hand for normal use I don't see it hurting anything.

Dick CNC is right as in that it is easy to reverse if I don't like it.

Yep nothing can really be hurt by this unless of course you crack the base casting. You might want to look at the underside of the base casting to see how much meat is there and look at the possibility of additional support or bolt holes.

By the way spacer blocks have been used on everything from bandsaws to Bridgeports. It isn't like this hasn't been done before on machinery. You already understand that this impacts the machine mechanically so why not try it out?

[wizard]

um no not everyone needs a haas but it's important to figure out what you need first then get a machine to match, picking one that you plan to have to modify from the start doesn't sound very logical.

On one hand I agree with you completely and that is why I suggest to people buying machinery to make sure it is big enough.

On the other hand sometimes you have to work with what you have on hand. Over the years I've seen everything from Kearny Trecker mills, to Pratt & Whitney deep hole drills to table saws to numerous lathes modified to solve specific problems. Was the engineer responsible for each of these projects wrong to modify the machine instead of buying a purpose built machine?

Sometimes economics dictates that you go with what some might see as a hack but it gets the job done and that in the end is what people are paying the engineer for. In this situation it will likely be a functional update to the owners machine as he already has a good idea as to the limitations involved. Sure another option is to sell and buy a bigger mill, but if the only reason you need that extension is to drill some holes does it really make sense to fork out a lot of money for that new mill when a few pounds of steel will do the job?

There seems to be a mad rush to condemn this idea. I have no idea why. This isn't even a radical mod and can easily be undone if the results are not acceptable.

[wizard]

OK so I don't ant more Z so I can Fly cut or even mill at the top of the column. I want it so I can "occasionally" raise it to drill a hole, drill bits and chucks take like 6" of the travel, turn a part on it's end and all of a sudden you need a WHOLE different mill just to drill? I don't think so. Just need to increase height for drilling now and again. Actual milling will be below the stock column height and as a benefit during normal use, say right above the vise, the column would indeed be stiffer as it is actually lower on the column.

You are going into this with open eyes, at this point just do it and report back your results.

Like 109jb pointed out, changing tools and lots of thing NOT involving cutting make increased Z height useful and you can do it without compromising normal height milling rigidity.

handlewanker, I wondered the same thing, I suspect cost would be the issue. But making such a thing for individual use is a different story. Surprised I have not seen it yet myself actually.

Honestly I see many of these modifications, some using lots of iron and I wonder why people just don't build a mill of their choosing from the ground up. After the significant investment in steel plate and tubing you might as well DIY a CNC machine.

I have an idea for a brace as well. Will likely fill the column and base with epoxy and heavy sand mix.

That might help vibration some but I'm not sure it will "brace" the column for you.

[bjones]

On one hand I agree with you completely and that is why I suggest to people buying machinery to make sure it is big enough.

On the other hand sometimes you have to work with what you have on hand. Over the years I've seen everything from Kearny Trecker mills, to Pratt & Whitney deep hole drills to table saws to numerous lathes modified to solve specific problems. Was the engineer responsible for each of these projects wrong to modify the machine instead of buying a purpose built machine?

Sometimes economics dictates that you go with what some might see as a hack but it gets the job done and that in the end is what people are paying the engineer for. In this situation it will likely be a functional update to the owners machine as he already has a good idea as to the limitations involved. Sure another option is to sell and buy a bigger mill, but if the only reason you need that extension is to drill some holes does it really make sense to fork out a lot of money for that new mill when a few pounds of steel will do the job?

There seems to be a mad rush to condemn this idea. I have no idea why. This isn't even a radical mod and can easily be undone if the results are not acceptable.

modding an existing machine you already have makes sense but this guy hasn't bought anything yet. hasn't defined what he even wants to make. all he's said this is for is for more drill bit clearance, on what who knows. if he's dead set on this machine and that's his only requirement he should look at getting screw machine length instead of jobber length bits.

[handlewanker]

Hi, I think the situation is an exploratory one with economics being the main game and possibly a pre used one lurking in the wings as well.

If that is so, then buying an X2 and modifying it is still going to cost some bucks, maybe even as much as buying an SX3 outright and converting it to CNC which is another kettle of fish when the project is finally costed up, but at least you end up with a stronger machine for the current needs.

No matter how you assess it, adding a spacer will give you the extra height to do what you intend it for, but if other factors arise, then you go on from there.

I 100% agree that height is prime real estate and a cheap bang for the buck , so now all you have to do is get the mill and mess with it.

The X2 is limited in most areas anyway, so the extra gain may be lost in the low specs of the rest of the machine.
Ian.

[NewHobby]

In all actuality I appreciate everyone taking the time to present opinion and offer insight. All of you are great and are only interested in helping and prevent someone from possibly making mistakes that are costly. Everyone means well and I appreciate it and I actually picked up some great information and perspective from all you guys.

I do have over a dozen parts I designed and had made by emachineshop online. Those dozen or so parts are representative of what I need, all of most can be made on a mini mill with no mods. The ones that can now would need more X travel than the 0704 has.

Getting a mill for prototyping is cheaper then having $300 one off items done over 3 times for refinements. I essentially need no more than the bf20 but simply done want to mess with the train wreck ways and scraping and jacked up dovetails. A dedicated cnc is optimal but I want to use a mill manually first to get direct experience. Thus I am left with the lms due to fit finish quality and performance envelope. Actually it is close to the x3's sans the z which I know I only need for an occasional drilling operation that I could see me needing.

Once you get into the 0704 type machine and factor your time a Tormach costs far less, at least according to the cost of my time. Since I am just prototyping and not doing any production work, and have a need to do so 2-3 times a year, thus the Tormach fully loaded cost is not warranted. But using the lms I could get going for $4000 with top shelf gear like gecko drives and control boxes all built and wired up like cnc4pc sells and so on and so forth and be up and running pretty quick all te3sted and ready to go.

I just got bobcat 26 and am learning that since I want to move from emachineshop cad and I needed a cam solution anyhow,bobcat fit the bill. Since I am learning that, I have a few months before I need to do anything. I just bought the 56" us general 450lb rolling tool chest with 3500 lb capacity last night to house the whole thing including the enclosure I'll build. Wholly crap that was fun Unloading with my 14 year old son, HF used a fork lift to put it I the truck. Actually I sold my tube bender to pay for it since I am done with it. Link to that project if anyone has collateral interests http://www.xs650.com/forum/showthread.php?t=27821


So actually I have thought about this for almost 2 years, took time to build a motorcycle from scratch first. My first post about building one was 2 years ago. I actually have a really good definition of what I need and a decision matrix on build vs buy and price relative to actual intent of use. There is no Abiquiu or honesty I. What I want or need. Any decision to go to a larger machine would automatically deep fault to just getting a dang Tormach and be done with due to hidden cost of time and haste with bigger machines. And even the I just don't need that at this time so I land back at the tight little LMS machine. If it turns out I do need more at a later time, I just get a Tormach or larger Skyfire and not even mess with a conversion and donate the LMS cnc to the kids high school.

Actually 50% of what I had made thus far were lathe based but that is a different story. here is a few that I have handy. So it is not QUITE as bleak as not having no experience or idea, I know pretty well what I need actually and I am well versed in all the choices from X2 through X3 variants including all the various brands like PM, IH, Optimum, busy bee, Grizzly etc...

Really what I need the the LMS since it has larger table and x/y with a just 2 more inches travel. That said I can make a rotating head, turn it sideways and drill that way. I saw some plan out here for that actually.

Cheers!

[bjones]

sorry but if you think a few people complaining about bf20 dovetails make them all a train wreck you are truly clueless. you better do more searching about the joke dovetails and gibs that are on these x2 machines. there are many complaints over the years about these things being warped, not making full contact, constantly needed readjusting, people looking for replacements in brass and so on. you recently asked an sx2 guy about his but you must have ignored his comment that he replaced many parts. in all your looking it seems funny you've never come across a taig, can't believe one of those guys hasn't chimed in either. a g0704 conversion cost doesn't come close to tormach either, you might be thinking of an rf45 which is much closer in spec and cost to convert. there are g0704 bolt on kits just like with the x2 and can use the same gecko control boxes you mentioned. the rf45's need to be custom made which is why the conversion cost and time to do it go up closer to the tormach cost. good luck.

[NewHobby]

Ok thanks. Been reading out here for years, clueless is kind of a strong word. Why take a chance is the point. Maybe the 45 class machine is where the cost is, but I sure know the grizzly 0704 is an absolute crap shoot with what you get. Not interested on 4 hard labor months and $1000 in tooling to do it right. This site is FILLED with 0704 builds so not interested is splitting hairs on who is right there. Pretty much know what I read and it is NOT once in a great while.

I know your gonna respond and say you don't need to do that, trust me "I" would need to do that. Enough on that.

I'd do an Optimum but the r8 conversion adds cost and the cost really goes up with that one, Enco here in the US has the for over 2k shipped. Then I read a handful of threads comparing it to a grizzly and their opinion was it was the same and the cost of the optimum was not warranted. Maybe that is the variability.

As far as the other SX2 guys mill, Ohh I saw and read it very clearly, he planned to buy the parts so he could work on them while having the mill working, and the parts are pretty cheap. They were not replaced due to some horrific defect.

As planned, I bought a replacement saddle from LMS for $65+shipping. They do a good job keeping parts in stock. Although I can’t completely justify it, at this point I also purchased another base (and another $65 spent) so that I could completely fit up the Y-axis, and by removing the two screws from the X axis bracket and sliding the table off of the mill, Icould mock up the entire X,Y assembly independently of the mill without much effort. It also allowed me to get the new saddle and base working smoothly together prior to the final machine teardown and CNC buildup. I went ahead and also bought a new set of x,y, and z gibs from LMS too.

http://www.cnczone.com/forums/bencht...version-2.html

Seen the Taig alright, but I want to do some manual machining first just to check off another bucket list item. Would be fun for 6 months or so.

Twas not a "help me pick a machine thread guys"

Thanks again guys I appreciate the time to lend opinion!