[will gilmore]

any progress? i really like this project

[mackeym]

Thanks jim_gieb and jalessi; i'm really looking forward to getting this thing running.

I've made some progress the last couple weeks. Thanks for your interst. I updated my website log just now (http://mackey-machining-rocketry.com/CNC%20Lathe.html). I think the loading time is getting long. I'll have to breakup the page into sections. In summary:

I epoxied in the first insert. It turned out that I didn't get very close to a 50/50 epoxy mix, so the epoxy never got very hard. I was able to pull the insert back out. To prevent this again, I made some steel plungers. They worked perfectly and the epoxy cured to be very hard. I received a 9/16" diamond core drill from UKAM. I decided to use what UKAM calls a "swivel adapter" to get water through the center of the bit. Rather than buying an adapter (for $150), I made one (for $35). It works perfectly except that i have some leaks if it is pressurized. The bottom of the core drill has two slits in it, so I don't leaking will be an issue (until the bit is worn past the slits).

Next step here is mass quantity hole drilling.

For the structural steel on the lathe, I'm going to cut up a 0.8" x 30" x 60" steel plate ($99 from HGR Industrial Surplus). I bought some grinder cutoff wheels and made an adapter to attach a grinder wheel to one of my AC servo motors. I'm going to use angle iron as guides to get straight cuts. I also layed out the cutting (in AutoCAD) so that only straight cuts are needed. Before I go any further on this, I want to get the rails mounted. That's all for now.

I don't have much time this coming up week (and weekend), but after that i'll hopefully have time to make some good progress.

[jim_geib]

Thanks for the update. I like your Idea for the inserts and the core drill.

Jim Geib
Mansfield, Oh

[nicad]

What are those smaller granite stones stacked on the end of the main slab (12"x18"x2" maybe?)? Are they headstock spacers? If so, do you know if they are parallel top and bottom to result in a flat + parallel top surface after stacking? If so, where did you get them?

[mackeym]

Those are 9"x12"x2" black granite surface plates from shars. Yeah, they are headstock spacers. The only precise flat surface is the top (and maybe the sides). The bottom has a rougher texture/surface finish, so unfortunately the top and bottom are not parallel to high accuracy (I don't know what the error is).

Regarding linear rails not being straight (before mounting), I called up THK and they did say that they are not straight in either the horizontal or vertical directions and mounting them to a flat surface with a shoulder surface makes it straight. I didn't think to ask how much error there is until after I called.

[mackeym]

Well, I have another update. http://mackey-machining-rocketry.com/CNC%20Lathe.html
In summary, the diamond core drill worked very well, and I was able to drill all of the holes for the first Z-axis rail.

Next, I'll make the inserts, glue them in, mount the rail, start on the second rail, and start cutting up a steel plate for the structural parts.

[sergizmo]

Thank you for the site showing the methods used in such detail.

I'm going to be using a granite plate as a machine base (much smaller though) and some of your ideas are very helpful. The wood template in particular is an idea that I will "borrow".

Great work!

Serge

[joeybagadonuts]

Mackey,

How long did it take to drill all holes for one rail?

JoeyB

[mackeym]

It took about 1 full day. Now that I have some practice, the second rail shouldn't take more than a 1/2 day. When the core drill is freshly dressed, it cuts pretty fast.

Regarding the wood template idea, I would guess that plastic sheet the right size (mcmaster has plenty of stuff that's pretty cheap) would work just as well (maybe better than wood...you don't have to worry about warping and it may be more accurate).

[jim_geib]

mackey,

Thank you for the up date, that core drill sure looks like the hot setup. That's a lot of hole down that plate, I don't think I will have that many in both of the rails on mine. What'ya gona do with all those marble columns? Oh yea, you never did say how you tiped that plate over, that had to be tense.

Jim Geib
Mansfield, Oh

[sergizmo]

It took about 1 full day. Now that I have some practice, the second rail shouldn't take more than a 1/2 day. When the core drill is freshly dressed, it cuts pretty fast.

Regarding the wood template idea, I would guess that plastic sheet the right size (mcmaster has plenty of stuff that's pretty cheap) would work just as well (maybe better than wood...you don't have to worry about warping and it may be more accurate).

I thought about that a while after the post. There is a local company called Canus Plastics that has a pretty good selection of random stuff for cheap. It's more the idea of a template rather than the material itself. It's such an easy way to space holes correctly.

Again, thank you for this thread and your site. The wealth of information on the Zone is amazing.

Serge

[mackeym]

Thanks everone for all the positive comments. I'm glad the website and this thread is useful. If it ever is not working, check back again a little later. I've recently been having some internet issues. Not sure if my cable modem is starting to go bad or if my internet service was down temporarily a few times.

Back to the CNC lathe. I think the obstacle of mounting linear rails on granite has been over come. Now it's a matter of doing the manual work of finishing the inserts, gluing, and repeating the process for the other rail.

[mackeym]

Regarding tipping the plate over. All of the things i used are shown in the 3rd picture down http://mackey-machining-rocketry.com/Base.html. I had 3 supports (two on the side and one in the center). I got the plate started by pushing by hand. The support in the center had an extended hydraulic jack, which i used to lower the plate a few inches onto the two outer supports. Then i moved the jack support down/back a little and put the jack back in place, raised the plate slightly, pulled the outer 2 supports back/down a little, and used the jack to lower the plate a onto the 2 outer supports again. I repeated the process a bunch of times. This is also how i got it upright in the first place.

[will gilmore]

are you going to drill and thread the inserts before epoxying them into the granite? if so I assume you can maintain enough accuracy to allow for adjustment of the rail. if not how are you going to machine them once they are in?

[mackeym]

I'm going to drill and tap after they're in. The only "premachining" I plan on doing is center drilling the leftmost and rightmost inserts. After they're all glued in, i'll first drill and tap the 2 centerdrilled inserts and then bolt the rail down with these two outermost inserts. To center the rail within the available play of these two inserts, i'm going to make a thin walled tube spacer. Then i'm going to use the rail to start the rest of the holes. I havn't decided if i'm going to center punch or drill (i'm leaning towards drilling now). Center punching is good b/c it doesn't produce any chips, but drilling i think will be more accurate (but will put some chips on the rail, which i'll clean off). After all the holes are started, i'll unbolt the rail and finish drilling and tapping the inserts.

If one or more of the holes end up with bad positioning accuracy (hopefully not), not all is lost. Depending on how far the positioning is off, the insert can be completely drilled out OR the bolt can be turned down a little.

[will gilmore]

you are doing the drilling of the inserts with the drill press? you could use a transfer punch to mark the center of the holes once you get the rail bolted in by the end holes.

[mackeym]

Yeah, i'm going to drill them with a drill press. Transfer punch is an idea. I think i'm just going to make a tube spacer and start the holes with a drill press and a twist drill bit.

[mackeym]

Another update. Not a lot of progress, but a little is better than none. I have the inserts for one rail made, and epoxied in 17 of the 25 for 1 rail. Then i came across a dilemma; the method of measuring out equal volumes of epoxy resin and hardener did not turn out to be as reliable as I hoped. Since the uncured epoxy is quite thick, voids and bubbles must have formed in the "measuring cups" throwing off the mixture ratio. I didn't realize this until after I glued 17 of the inserts. 5 or 6 of the inserts may need to be drilled or pulled out and replaced. A quick google search for "anchoring epoxy" showed that there are many other epoxies for anchoring metal into concrete/stone. The consistency tends to be thick and pasty, and the two components are usually white and black giving a final gray color. I suspect I'll have similar issues with any of these other types. It's not easy to get small and accurate 50/50 mixture.

I called Tru-Stone technical department, and they recommended Devcon 2-Ton epoxy (local hardware stores tend to have this). He said that he sometimes uses this. Tru-Stone's standard epoxy is proprietary, so they couldn't give any information on it. The guy mentioned that the thick anchoring epoxies do not adhere to the granite as well as thinner epoxies since the thinner stuff more easily penetrates the pores.

I'm going to finish gluing in the remaining inserts for this rail with this new epoxy, then drill and tap all of the inserts. The concern with the not-so-hard epoxy is that when the rail is bolted down the inserts may slowly shift. What I'm going to do is find the worst epoxy sample, and test it to see if the corresponding bolt needs tightening after a day or so. If the bold does not need tightening, I'm going to leave them as they are for now.


http://mackey-machining-rocketry.com...0Mounting.html

[jalessi]

Hi,

Check out the link below, this stuff works awesome and has mixing dispenser.

http://tinyurl.com/68veqt

Jeff...

[mackeym]

After having a little trouble with the epoxy and inserts, I decided to make some changes and try some tests (something i should have done in the first place). The tests turned out really well..these inserts won't come out under any torque (the 1/4-20 socket cap screw shears before the insert pulls out).

I drilled 4 holes into a small black granite plate (these core bits really work well). The inserts were 304 SS, 1.500" long and 1/2" diameter. Two of the inserts were left with a smooth outer surface. For the other two inserts, I turned a 20 TPI thread on the outside. When making the OD thread, i angled the 60o thread-bit a little so that the thread is kind of like a barb (I don't know if this helped any).

For epoxy glues, I tried two types: Devcon 2-ton and Loctite metal/concrete

Before i glued the inserts in, I cleaned them with some real cleaner (BIX TSP it's a degreaser and cleaner mainly for preparing nonporous surfaces for painting). I did not touch the inserts with my bare hands (wore vinyl gloves) after they were cleaned. Any kind of oil is not good for the epoxy adhesion.

The inserts were drilled and tapped for 1/4-20 screws. I made a small aluminum piece for testing the insert pull-out strength (did not use a linear rail).

The plain insert glued with Devcon 2-ton broke loose along the epoxy-insert interface at about 85 lb-in torque. For the other three inserts (plain insert with Loctite metal/concrete, threaded insert with Devcon, and threaded insert with Loctite) they were perfectly fine way past 210 lb-in...and the bolts broke.


One more important thing. I previously glued in a few more of the inserts (with the groove pattern shown in my website) into my big granite plate with Devcon 2-ton and they did not hold up (broke along the epoxy-insert interface). This means that the thread type groove pattern is much stronger than the groove pattern i previously used.

It seems that the Loctite metal/concrete epoxy has MUCH better adhesion to 304 SS than Devcon 2-ton. I did not have any break at the granite-epoxy interface, so I think both epoxies have adequate adhesion to black granite.

In spite of what the Tru-Stone guy said, I'm going to go with the anchoring Loctite epoxy. Devcon 2-ton does not have very good adhesion to stainless steel. I think any good quality epoxy will work very well as long as the OD of the insert has a thread pattern, the epoxy is well mixed in the right proportions, and the insert is clean (absolutely no oil or grease). I turned the threads on the insert with no lubricant to keep the amount of oil on the inserts to a minimum.


I solved the problem with getting inaccurate proportions of resin and hardener for the Loctite epoxy by measuring by weight. The funny thing is...is that i got the data sheet for Loctite metal/concrete epoxy, and it said that both the resin and hardener had a specific gravity of 1.6. Since the densities are the same, a 1:1 weight would be the same as a 1:1 volume ratio. I didn't find this to be the case though. I used very primative technique for testing the cured epoxy--the finger nail technique. If I am able to make a mark on the cured epoxy with my fingernail, it is not as hard as it should be. I made a small series of samples, and the right mixture by weight seemed to be 33 to 38% of the black component.


Back to my build, I need to drill out all of my inserts for one rail (these either have inserts with soft epoxy or Devcon 2-ton without a threaded OD pattern). I got two 9/16" hole saws (one HSS tipped and one carbide tipped). Then i'm going to lengthen the holes a little so i can use 1.5" long inserts instead of ~1.1" inserts.

The only uncertainty now is whether Loctite metal/concrete epoxy adheres to pink granite as well as it does to black.

Those who waited for me for an insert technique...you should have no problem getting super strong inserts. Make sure you do some tests first!! I don't think drilling out these inserts will be fun.

Sorry for such a long post, but I think there is some good info in it.

I just thought of a few more things that weren't mentioned. When I glue in my new inserts i'm going to use a decent clearance between the top of the insert and granite plate (0.04" to 0.06"). It doesn't pay to try to get it very close, and it is a pain to fix if the insert ends up above the granite plate surface (I had this problem with one insert). I did not find it possible to get a hole depth accuracy greater than about 0.05" because the core doesn't always break off at the very bottom. Because of this, it's better to drill the holes first and make the inserts second.