New Stand for RF-30 CNC Mill Drill Conversion

[Meganick]

Anybody have photos, plans or recommendations for replacing the stock RF-30 (Harbor Freight) sheet metal stand?

I am just getting the XY going on my new conversion and it seems like my sheet metal stand is not rigid enough, especially with a 90 lb vise attached to the table. If you lightly push on the top of the RF at just the right rate (with the controler power off), you can build up a resonance where the whole machine is shaking. Inverted pendulum. Taping the jog key on Mach 3 causes a similar effect. It is proably usable without the vise in place.

Am I look at pouring a concrete pier for the base? short of that, has anybody had good luck with welding up a square tublar frame?

-Nick

[Bubba]

I did mine out of a weldment of pipe, plate, and angle. Was built several years ago and also included leveling feet to take care of any in accuracies in my concrete floor. Place an "oil drip pan" on top of that to catch coolant and swarf and the mill is on top of that.
Has worked quite well.

However having said that, if (when) I redo it, I will make it wider for even greater stability. Right now, it is basically 4 legs (braced) with a footprint of your sheetmetal stand.

[Meganick]

Bubba - I'd love to see some photos.

Any problems with a machine vise on the table? Not ROCK solid?

A wild thought: how about making the stand out of reinforced concrete? Use chicken wire and light rebar. If you roughly take the shape of the sheet metal stand and made it out of concrete, it would weight about 1200 lbs. To lighten it up a bit, add some foam block in the center to make it hollow. 500-600lb would be nice. Sakrete costs about $7 for an 80lb bag. Thats a cheap way out and when you move, you dig a hole in your yard and bury it.

I was thinking about plywood forms to mold the stand. But what if the Sheet metal stand itself was filled with concrete, again with a hollow foam core to get the desired weight? I don't remember what the inside of the stand looks like. Where there compartments?

Sounds like the stock sheet metal stand doesn't cut it. I'm kind of headed down the weld up a new frame path (or concrete?), but I'd really like to know if people tossed their sheet metal stands 'cause they didn't cut it. Or were they just smart enough to know not to buy the sheet metal stand in the first place?

-Nick

[Bubba]

Meganick,
As jammed in as my setup is, I can't get any good photos now and I don't have any from when I made the stand up several years ago.

I don't really have any problems with a big 6" Kurt clone vice on there. Any problems I have are generally related to stupidity and ignorance on part of the operator.

It is basically 1 1/2" pipe on the four corners vertically (should have splayed them some) with about 2" angle that runs across the top on the fron and back. Then some 1/4 x 4 plate that ties the fron and back together and about a third of the way up from the bottom, I welded a cross brace on the front set of legs and again on the back. Then another was welded to connect the midpoints of these braces. For leveling, I welded plats to the bottom of the legs that are drilled and tapped for 1/2" althread. Nuts are welded to the bottom so I can use a wrench to adjust the legs and locked down with lock nuts.

Every once in a while, I have to tighen up the adjusters because of vibration etc. I have thought seriously about reworking it and bolting it the concrete floor to make it more rigid.
I like the idea of a "space frame" to support the mill because:
1. I have a hole (about 4" dia) under the center of the mill which is for acess to the Y axis ballscrew.This is coupled with a drain for coolant to my coolant sump.
2. I also "tucked" the Y axis servo under the mill so it is also in this space. This gets it out of the way and also protects it some what from swarf and coolant!

I do agree a concrete base would be ideal from a mass and stability standpoint, but I would also have lost the acess to the bottom and space for the servo in my case and that would have been a big loss based on my experience.

[Bubba]

Meganick,
While surfing around this afternoon, I ran across this link of an excellent stand done by Bob Warfield! Solid and should do the job and even has a drawing to get you started. It is for and IH mill, but the principle is the same.

http://www.cnccookbook.com/MTWeldingMillStand.htm

Excellent site with lots of good information.

[Meganick]

Hey Bubba!

Thanks for the link. That's some kind of stand! Now if I can find a local source for 2x4's and 4x4's.

Like you said, also good source of info on the site. I also saw some good religion on Angular Contact Bearings too.

Any idea what the wall thickness was on your stand's uprights? like 1/8?

I dialed back the acceleration /deceleration on my machine to 1 in/sec/sec as a temporary fix. Takes a long time to get moving and a long time to stop when you are jogging it. At least I can make some metal chips, but I really need a long term fix...something like the stand you built.

-Nick

[Bubba]

Meganick,
I used Sch 40 pipe for my legs and braces (I worked for a fire sprinkler company and had dumpster privileges:})

Mine is 1 1/2" pipe for the legs as that is what was in the dumpster at the time. BIGGER is better! Who knows what will be in there the next time?

[bentwings]

Pretty cool pictures. I assume there are some adjustable feet for leveling. I'm sure glad to see there is someone else that uses a Tig welder for everything even though they are expensive to operate. If it's what you have ya gotta use it. Welds sure look nice when they are painted.

[ballendo]

Hello,

Go to the yahoo group mill drill and look for the details of adding 2 bags of ready-mix concrete into the base of the existing stand.

For me it was Like night and day; just as the original poster of the mod said!

There is NO wobble and NO flex any more.

To save you the lookup, i'll just say that I used a piece of 3/4 ply held to the bottom of the base with 1/2-13 threaded rod (one 3' length cut into 4 pieces and 4 long connector nuts ; which I embedded into the concrete inside the stand. The existing threads for leveling may or may not match 1/2-13; but they're easily modified to fit that. I ran a tap through them and then "screwed" the Th. rod into each one from the TOP SIDE of the base. (that way when all 4 were just proud of the bottom surface I could lay my ply against and rap with a hammer in the 4 spots to make a mark to drill for the rod to go through the ply.

Continue screwing the rods into the connector nuts--these will provide the new threads for your adjusting feet!--until you can get a nut on the bottom to hold the ply on. Be sure to vaseline or oil or grease the screw and connector nuts. I set the connector nuts flush at the bottom of the base, right against the ply before adding the concrete.

Now you have the rods through the original threads of the base (and sticking out the top of the wide parts OF the base), then through the new connector nuts, then through the ply, then through the nuts which hold the ply on.

Now you get some short rebar at home depot and some iron baling wire and wire a "tic-tac-toe" grid from 4 pieces and set this aside. You could use other things instead and/or in addition to the rebar.
Just be sure you have some reinforcement built into the concrete for when you drop the stand!<G>

Turn things right side up and mix up your first bag of redi-mix concrete. Pour it in and spread it around completely filling the areas around the new nuts and under the wide spots at each side. Level it a bit and then put the rebar into place and add the second bag of ready mix. That's it. Let it cure and keep it wet for a few days...

You WILL be impressed. It works AMAZINGLY well. (I kinda did it just because I couldn't believe it could actually make that much difference.) But it does!

My CNC RF-31 moving at over 150IPM was not only quieter; it was making better parts.

DO THIS MOD...

Hope this helps,

Ballendo

P.S. I'd show pics but many pieces of equipment in one of my shops were stolen recently; including this mill. I hope to be replacing it this week; and will be doing the stand mod again; so if you wanna wait...<G>

Originally Posted by Meganick Anybody have photos, plans or recommendations for replacing the stock RF-30 (Harbor Freight) sheet metal stand? I am just getting the XY going on my new conversion and it seems like my sheet metal stand is not rigid enough, especially with a 90 lb vise attached to the table. If you lightly push on the top of the RF at just the right rate (with the controler power off), you can build up a resonance where the whole machine is shaking. Inverted pendulum. Taping the jog key on Mach 3 causes a similar effect. It is proably usable without the vise in place. Am I look at pouring a concrete pier for the base? short of that, has anybody had good luck with welding up a square tublar frame? -Nick

[Meganick]

Ballendo - thanks for the info - I sort of understand what you did. Wish I had some pics. But what I hear you saying is that the sheet metal stand
is strong enough and does not need to be reinforced. The real part of the fix is to add mass at the very bottom of the stand. When you are done,the plywood sits between the base and the floor and you have a layer of concrete on top of it inside the stand? The leveling screws are retapped
and secure the plywood to the stand. Are there leveling pads under the plywood and does the machine end up resting only on the leveling screws?

Sorry to hear your equipment was stolen. Post new pics when you get replacements.

-Nick