[osiervt]

First this place is awsome the amount of data and resources here is just amazing to me. A month ago I would have never dreamed of takeing on a project like this, however with the amount of reading I have done here learning from what others have done I am fairly confident I can do this project.

I'm going to add a twist to the standard build you see in this area though. I'm going to Attempt to use Expoxy Granite (EG) build the base of my router. The guys on this forum have been working on this stuff sence 2007 over in this thread, http://www.cnczone.com/forums/showth...30155&page=339. If you havent read it yet I suggest it, be warned it is currently 339 pages and growing! It took me 12 hours of reading to get through it all but i learned ALOT. I just have a rough sketch of what i am intending to do right now. A lot of the details still need to be drawn but I have a long way to go before i get there.

Tomorrow I will be calling around to order the required materials to build the base. With the weight of the materials they will go ground so I have at least a week till I can expirement with small batches of EG. I will make several small parts to get the technic down before attempting "the big pour". I will document all my trials here as well as over in the EG thread so that others may learn from what I am doing after all that is what this place is all about.

I generally intend to use this for wood working but if Im going to do a build i might as well make it strong enought to handle harder materials too. I have taugh my self several leasons over the years about getting cheap tools. They always end up causeing me headaches and I upgrade in the end. So why not save money and go all out the first time.

Any way below are a few images of what I intend my build to look like. As I experiment with EG I may revise them but this is what I have in mind. Feel free to commit and give advise. If you have any questions please ask, I am just learning this stuff but I think I have my head around it and will do my best to expain what I am doing.

[brunog]

Osiervt,
Interesting project!

I have a question:
Why is the gantry made out of MDF and not EG ?

And a few remarks:
The support plates should be embeded in the EG casting and held by inserts, either welded or bolted to the support plates, this will simplify the casting process. The support plates should be have drilled and tapped holes to enable fastening of the linear rails,

Be careful with chamfering and pointed areas, they will hard to properly fill when pouring EG in the mold and edges with sharp angles are easy to break/shatter.

Good luck with your project

Best regards

Bruno

[osiervt]

The gantry is MDF mainly because I was concerned about the weight. After playing with this stuff I may change it to EG but I figured by makeing it with "walls" of EG and eliminating the uprights of the gantry a lot of the stress on the gantry would be eliminated. Thus i figured I could get away with MDF with out getting to much flex.

I am planning of drilling and taping the support plates to secure the linear rails after the casting process. I figure by waiting to drill and fasten the rails it will allow me to better align them. Maybe that is not as difficult as I am makeing it out to be and could get away with doing it before hand. These holes are one of the details I didnt draw yet. I will try to add those details today.

My reasoning for using the through bolts instead of inserts for the gantry rail mounting point was using the through bolts would put any lifting pressure on the bottom of the base compressing it upward. I figured this would be much stronger than a insert set a few inches deep. But I may be over building at this point. I will look through the McMaster catalog a bit more today and see what I can find for inserts. A quick look found these. http://www.mcmaster.com/#threaded-inserts/=84kp0b They are only 3/4 deep and thought, but im sure they have something that would work better.

I see your point on the points I will work on smoothing out the structure as well. The points would also have caused stress risers.

Thank you for your tips.

[brunog]

There are many drawbacks in drilling holes and setting inserts and suport plates after casting:
1-The use of special tools for drilling
2-Handling of a >100 lbs casting vs lighter and smaller individual pieces of plywood (or mdf) when drilling
3-Smaller footprint inserts set in epoxy vs larger ones casted in EG
4- Extra mold parts embedded in EG in place of actual support plates

Best regards

Bruno

[RomanLini]

Nice idea, I like the simplicity of a cast U-shaped base and a simple beam gantry.

However I would suggest swapping out the MDF box gantry for a square steel tube (box) possibly welded. Your MDF gantry is not particularly easy to build and suffers all the problems of MDF as a construction material. Steel tube will be strong and lightweight, and you have the very easy options of filling the steel tube with epoxy granite or a lightweight epoxy composite.

[ckelloug]

Hi there again osievert.

I'd recommend you read the paper posted by edubravic in EG thread post 4052.

The direct URL is http://dspace.mit.edu/handle/1721.1/9373

This will give you a good background in why Bruno made the suggestions he did. It's an MIT paper and it's excellent!

Regards,

Cameron

[osiervt]

Hi there again osievert.

I'd recommend you read the paper posted by edubravic in EG thread post 4052.

The direct URL is http://dspace.mit.edu/handle/1721.1/9373

This will give you a good background in why Bruno made the suggestions he did. It's an MIT paper and it's excellent!

Regards,

Cameron

I'll read that over the next couple days, just flipping through it, it looks like a great read. I've tweaked my design a bit already and cut down on the size a bit to reduce the weight to something a bit more managable. I got really rough numbers using the packed density numbers on the Quartz from Agsco's site, with those numbers the new design will weigh in at 313lb the gantry would be 46lb!

[SeanB]

Hi Osiervt,

I have been lurking around the forums for a month or so and I am looking to produce a similar type of gantry machine.

One suggestion for a light weight gantry structure could be to laminate thin composite skins either side of a ply core. You can buy these pre-made or they can be fairly simply produced (although vacuum bagging is recommended). You would also lay up some angles against an extrusion to produce joining plates. The whole structure could be then bonded together and sealed with epoxy to avoid any moisture issues. This would dramatically increase the stiffness.

Good Luck.

[osiervt]

Sean,

The thought of using composites had occurred to me before I ran across the Epoxy Granite thread. I'm in aviation and have had experience with layups and vacuum bagging. However Flex was a concern when I was looking at using it for structural pieces however if it was used just to reinforce the part such as the MDF gantry I would see no harm in it. It would actually serve as a god protective layer to, protecting the MDF from fluids and such. The other concern besides flex was composites are very susceptible to impact damage. Seeing how this is a machine tool in a garage I didn't see composites going over to well

[osiervt]

I'm starting to figure out why epoxy granite counter tops are so expensive... I'm calculating the volume of my base to be 7200 in^3. Using Ckelloug's formula from the epoxy-granite thread and the prices I have be quoted I get the following:

Note: stone comes in 25lb sacs and the zeeospheres come in 50lb sacks so.

Calculated for 7200in^3:

0.312 Agsco #6 Al2O3 -- $1.342/lb * 320lb needed = $469
0.206 Agsco #4 Quartz -- $0.50/lb *65lb needed = $37
0.101 Agsco #2 Quartz -- $0.50/lb * 32lb needed = $25
0.183, Agsco #2-0 Quartz -- $0.61/lb * 58lb needed = $45

This part kills me due to the qty discount, Im playing phone tag with the distributor right now but using numbers Cameron posted, its cheaper to buy 250lb than 100lb!

0.111, G800 Zeeospheres -- need 63lb 100lb for $595 or 250lb for $422.50
0.087, G200 Zeeosphere -- need 56.6lb 100lb for $610 or 250lb for $470.

Don't forget $290 for the 7.5 gallon 635 epoxy kit

So much for my budget... and now I know why Walter said he had a life time supply of zeeospheres on the other thread

Also recalculating for the densities and qty of each material based on this formula the base alone would weigh in at 594lb of aggregate plus 4 the wieght of nearly 4 gallons of epoxy (I couldn't find the density of the epoxy)

[ckelloug]

Hi osievrt,

The density of epoxy is about 1 g/cm^3 depending on the exact epoxy and hardener and shouldn't vary by more than about 10%. This amounts to about .04 lbs/in^3 or about 8.4 lb/gallon.

In that the Al2O3 is more expensive than I remembered, you might see if Agsco can produce some quartz that is graded like a #6 abrasive. I originally used used Al2O3 because it is naturally sold in this size at Agsco, Walter liked it, and it has a much higher fracture toughness than quartz.

Also note, that when vibrated, the mixture from my current reference formula should theoretically compact down to about 11% voids which means that 89% of the volume of the machine should be solids and 11% will be epoxy to fill the voids. I believe the calculation for the most part but I haven't done the experiment yet to check for exact values.


Also, you may want to think about putting foam or a steel tube inside of some of your structures to minimize the amount of E/G used.

Regards,

Cameron

P.S. If it's any consolation, I probably could have bought a used vertical machining center for what I have invested in equipment for developing my own E/G formula.

[osiervt]

I'll look around for for an AL203 replacement, I was curious if it served a particular purpose. I found an awesome deal on a vibrator last night too, a Cougar ABF-35 for only $40. Its air driven and at 40 PSI vibrates at 8200RPM which is right around the right neighborhood according to the paper posted by nebbiasound over on the other thread. Here's a link to the spec sheet on this, Spec Sheet.

As it stands the walls are only 3" thick so putting an inch of foam in the center may make the walls to thin? 500lb just for the base is going to just be to heavy. I would hate to have to move something that massive. I may look at making a 1.5" steel square tube "lattice" filled with EG walls. This should be strong enough and with the EG heavy enough not to vibrate. These thinner walls will knock 3" off the width of the base with out losing any work area, that would put the base in the ball park of 327lb plus what ever my lattice walls would weigh. Much more manageable. I will play with this a bit tonight, the wife is going to be out so I will have time to play

You may have enough tied up in EG stuff to buy a milling machine center but just think of the fun and mental stimulation you have gotten for the EG project. That is some thing you can put a price on.

[osiervt]

I finished reading the MIT paper on machine tool design and I have to say it was fantasic reading. I tweaked my design to incorporate some of the aspects and recomendations in that paper. It is not complete nor is the design perfect yet, but I believe it is much improved.

With luck my vibrator, quartz and epoxy will all be here early next week. Once the stuff arrives I can start experimenting and playing! I cant wait! Until then I will continue improving the design and rereading some of the papers to see I can pick up some thing I missed the first time.

[ckelloug]

Hi Osievrt,

Your machine design is looking pretty cool.

I have the following comments:

From my reading of the MIT paper on design, you might be better off making the embedments stand proud of the E/G surface so that they can be made precisely flat by precision grinding or precision scraping. If you make the embededments out of durabar or versabar which are continuous cast iron, this will simplify the scraping process if it needs to be done. I'd think 3/4 wide, 1-2 inches deep for the length of the way surface would be fine.

In this way, you can tweak the exact parallelism and planarity of the x axis ways to which the linear bearings are bolted as well as ensuring perpendicularity between the xy plane and the z axis. Rather than scraping, it might be possible to have the both x rails ground in one step on a large way grinder but this may turn out prohibitively expensive. It may also be possible to have the mounting surfaces for the rails precision ground by a machine shop with a large surface grinder before casting these parts into the E/G.

Another reference which I am familiar with is Precision Machine Design by Alexander Slocum at MIT. It would suggest that if the loads allow it that you use only one linear bearing block on one of the sides to minimize linearity error due to overconstraint of the x axis in the y direction.

The third comment I have is that your previous drawings showed you driving the X axis from one side of the base. This may cause the linear bearings to bind. It may also cause position errors due to torque on the beam around the z axis due to unavoidable bearing play. Ideally, I would think one would want to drive the X axis from both sides or maybe from a yolk under the C/G to minimize this effect even though in practice, I don't know how bad the effect is but it is mentioned in some of the linear bearing handbooks.

Instead of a plate, why not just put 2 parallel bars like those on the x axis on the cross beam. They're lighter and serve a similar purpose as well as providing a narrower area that needs to be precisely flattened for linear bearing mountings.

The reinforcement plates you show probably need to go between the linear blocks and the E/G beam, not on top of the beam. In general, I believe the MIT paper suggests embedments need to be surrounded with E/G on all sides except for the protruding side.

Finally, it may make sense to counterweight the beam with the z axis and spindle installed so that there is no net torque around the y axis as it moves. This will help keep the beam from vibrating as there will be less tendency for a stick-slip action as the x axis moves. If you don't balance it, the linear bearings will be forced to constantly provide a force to keep the beam from rotating and it may have an action on the microscopic level like the bow of a boat alternatively digging into a wave and then riding over the next wave. Your design mitigates this problem some since the center of gravity will ultimately be between the linear blocks but it is something to be mindful of.

Hope these comments are helpful.

Regards,

Cameron

[osiervt]

I'd think 3/4 wide, 1-2 inches deep for the length of the way surface would be fine.

Your suggesting embedding the x axis linear ways perpendicular to the top of the walls using 3/4" thick plate instead of using a 1/2" with the bolts on the bottom embedded parallel like I have them now? By going deeper with the metal plates would this not increase the thermal expansion problem of the two materials expanding/contracting at different rates?

In this way, you can tweak the exact parallelism and planarity of the x axis ways to which the linear bearings are bolted as well as ensuring perpendicularity between the xy plane and the z axis. Rather than scraping, it might be possible to have the both x rails ground in one step on a large way grinder but this may turn out prohibitively expensive. It may also be possible to have the mounting surfaces for the rails precision ground by a machine shop with a large surface grinder before casting these parts into the E/G.

When I read the part of the MIT paper about the grinding of the ways money signs flashed in my head. So maybe naively I came up with a cheaper solution that may or may not work. My thoughts for getting these adjustments without involving special tooling was to drill the mounting holes for the linear rail until after the casting process. After casting using a center punch, square and drill mount one of the rails exactly parallel with one wall. Then use a cross beam with a linear rail cartridge mounted firmly to the bottom at each side to evenly space and mount the opposing rail exactly parallel to the first rail. To get everything coplanar I was thinking of using delaminable (spelling?) shims between the rail and the ways.

Another reference which I am familiar with is Precision Machine Design by Alexander Slocum at MIT. It would suggest that if the loads allow it that you use only one linear bearing block on one of the sides to minimize linearity error due to overconstraint of the x axis in the y direction.

Over constraint never occurred to me I will have to look this paper up.

The third comment I have is that your previous drawings showed you driving the X axis from one side of the base.

I’m aware of the racking issues, you caught me being lazy in my last drawings, way to call me out on it I figured with the angle I took the screen shot at no one would notice I never drew the opposite screw. When I redraw the drive system I will draw it on both sides in order not to cause confusion on my intent.

Instead of a plate, why not just put 2 parallel bars like those on the x axis on the cross beam. They're lighter and serve a similar purpose as well as providing a narrower area that needs to be precisely flattened for linear bearing mountings.

Instead of trying to find a good deal on a set of linear rails I was thinking of using CNC parts linear trucks to construct the Y-axis. This is the reason for the large plate that extends off both sides. Watching the builds here many people have used these with really good results.

The reinforcement plates you show probably need to go between the linear blocks and the E/G beam, not on top of the beam. In general, I believe the MIT paper suggests embedments need to be surrounded with E/G on all sides except for the protruding side.

In the paper where they mounted their two sections together they put these plates on the bolt head side which is what I did here. Unless I read the paper work which is possible the reason for this was to spread out the pressure of the bolt head over a larger area of the EG, thus reducing stress. I will look at this again though.

Finally, it may make sense to counterweight the beam with the z axis and spindle installed so that there is no net torque around the y axis as it moves. This will help keep the beam from vibrating as there will be less tendency for a stick-slip action as the x axis moves. If you don't balance it, the linear bearings will be forced to constantly provide a force to keep the beam from rotating and it may have an action on the microscopic level like the bow of a boat alternatively digging into a wave and then riding over the next wave. Your design mitigates this problem some since the center of gravity will ultimately be between the linear blocks but it is something to be mindful of.
Hope these comments are helpful.
Regards,
Cameron

I’ll look into this last bit. As always thank you for the observations.

[ckelloug]

Hi Osievrt,

I think you were on the right track, I just didn't quite understand what you were trying to do.

Your probably better off with the 1/2in and the bolts on the x axis inerts as it gives a positive lock to the E/G. I couldn't tell on your drawings what the thickness was. You're right that a bigger embedment does increase internal stress from thermal expansion. It's still possible that it could make things easier to leave the insert sticking up from the E/G a bit though if you have to use drastic measures.

My comment on griding or scraping after embedding wasn't to help the xy alignment which your predrilling will, it was to help with ensuring that the surface on which you will mount your rails is dead flat rather than lumpy. The shims may work for this instead depending on the accuracy you're trying to achieve but you end up with tiny unsupported sections of linear rail that way.

Having the bars precision ground before embedment wouldn't be terribly expensive, having the whole assembly ground with the bars in place like the paper recommends would be expensive and isn't on my list right now either. Precision grinding before embedment won't help as much as one would like however unless the mold keeps them exactly coplanar and flat.

The linear trucks you want to use sound great. I haven't seen them so I can't comment. I was curious why you were doing it that way.

If you are going to through bolt the detail I commented on about the rail then it certainly makes sense to reinforce the bolt head side. I didn't realize that you were going to through bolt it. I thought that the linear rail blocks just had tiny screw holes in them in which case they can just be screwed to an embedment on the block side to be able to put in the threads and holes for the tiny screws.

Finally Precision Machine Design is a book by the professor who taught the guy who wrote that paper we've been discussing. [ame="http://www.amazon.com/Precision-Machine-Design-Alexander-Slocum/dp/0872634922"]Amazon.com: Precision Machine Design (9780872634923): Alexander, H. Slocum: Books[/ame] It's expensive but you might be able to find it in a library.

Regards,
Cameron
Making the simple complicated and the complicated simple in E/G since 2007.

[osiervt]

I found the precision machine design book, free too. Gotta love google while at the same time be deathly afraid of their indexing and data mining power.

Precision machine design By Alexander H. Slocum

Its a limited view book you get to view 150 pages or so then it cuts off. But if you go back to it in a few days and skip the pages you read the limited view shows you different pages. Gotta wonder how google gets around the copy right laws with this stuff. Any way its there for all to read.

[PrecisionSpindl]

If you are considering grinding on a way grinder, and interested in a quote -

Precision Spindle & Accessories Inc.

www.precisionspindleinc.com tel. 519 671 3911
[email protected] fax. 519 652 5994

[osiervt]

If you are considering grinding on a way grinder, and interested in a quote -

Precision Spindle & Accessories Inc.

www.precisionspindleinc.com tel. 519 671 3911
[email protected] fax. 519 652 5994

When i get to that point I will let you know.

[osiervt]

Well today was interesting. I started this morning off by learning my company is getting bought out and will be going through a merger over the next few months! That is some way to start your morning hun? But hopefully it will work out for the best.

I did get my epoxy in today. I dont have my vibrator or quartz yet but i have a cup of granite chunks and play sand mixed up in the garage for the heck of it right now. Time will tell how it comes out.