Weelding the gantry for a better tool?

[roy_shimp]

I have a 2000 PRT and been reading the threads on how folks have been welding their shopbot for better performance (stability), however i don't yet get exactly needs to be welded. Good pics, but they seemed to be upgrading the machine instead welding the existing machine at certain points. What are the points of welding and what extra metal do i need to buy to strengthen the shopbot? Step 1,2,3... Thank you. Roy Shimp

[donclifton]

Don't weld, steel moves a lot when welded and more likely then not it will be out of sq. I use to weld everything but when I got into building CNC machinery I bolt everything.
Thanks
Don

[garyb]

The Y carriage on the prt's have 1 bolt on each corner which has a tendency to move with cutting force thereby knocking the carriage out of square. A tack weld on the 4 corners will take care of that problem.

[roy_shimp]

Donald - thanks, if i tack before welding will the gantry/machine still get out of square?

Gary - Thanks, what is the downside of adding support beams in various places (thread of August 27, 2005)? Did i misunderstand something?

Thanks guys for the feedback.

[donclifton]

I would add an extra bolt in the corners. Your gantry is driven from both sides and has no reason to get out of sq. any time you heat steel unevenly its going to move. I wouldn't do it but that my 2 cents.
Thanks
Don

[gc3]

You can help stop some of the weld heat transfer by placing a damp rag on the under side of the area you wish to weld. These would be short welds so heat transfer would be short lived....I think



Gene Crain
www.plantasymaderas

[navigator7]

I'm with Don regarding welding. Steel moves a lot when welding. The tendency is to weld more than less because you have a wire feeder or a handful of rod.
The other thing about welding is location location location.
A tack in the proper location could be used the lift the machine off the ground.

I once laser aligned a 1200 Hp water pump to its frame bed weld alone.
The final pass still moved the pump!

Therefore, Gary suggestion about a "Tack"....a real tack, not a bead is not bad either.....IMHO.
The important part is placing the tack so it is functional, removable and doesn't cause make the machine pull itself out of square.

Do triangles of threaded rod, or turnbuckles have an application here?

The part I'm missing is where is the complaint? What is moving? Does your machine work ok, Roy??

[coach]

If I recall, welding steel uses D.C.Reverse polarity. The electric current will go through everything that is grounded by your ground clamp.
Watch out for arcing in places such as roller bearings. For a heat sink, if you have some 1/4" alum or copper that will fit behind the area being welded.
As suggested by Chuck not pulling out of square.
I always thought in terms of counteracting forces.
If you place a thin piece of rubber under the rollers you could save some problems too.
I know guys have welded their bots but just my 2 cents.

I would also be very leary of my electronics.
I welded for 25 years and wrecked some stuff.

[joe]

Every quality CNC on the market, that I've seen, is welded.

The old PRT I once had needed stiffening up so we tack welder her together. It helped with the wobble.

Un-hook all electrical conections first.

[donclifton]

Joe, thes quality machine don't run on angle iron rails but linear rail that are not welded to the frame. I bet if you call the manufacture that they would tell you the frames are heat treated and relieved. The rail way pads are then machine level and true to each other. I just hate to see someone screw up a machine that just needs a little alignment. If the gantry is twisting it is because the rails are not running parallel at that point. Both sides of the gantry is powers evenly by steppers.
If you just have to weld, get some scrap angle and clamp it down sq and give it a test run, it will move. Large router manufacture have a lot of resources I sure you don't.
Thanks
Don

[navigator7]

Hi Joe,
There nothing wrong with welding.
In the big picture....welding occurs, then the normalization process like heat treating, then machining and the ginger bread like hardened rails are installed.

I've yet to hear what Roy's complaint is?

That he hasn't welded is machine already and introduced himself to an unnecessary learning curve is good.

If his machine is moving, creative use of a dial indicator and two c-clamps and a diagonal stick will tell him instantly.

Al he needs to do is create a file that shakes the machine and run it in space.

[garyb]

My mistake the y carriage of the prt does have 2 bolts in ea corner not 1 as I stated before.
Either way these y carriages can experience movement within the frame which causes them to lose square alignment.
There's no need to lay down a fillet weld and destort the fame as everyone appears to be getting so exicted about, just simple tack weld at each corner is sufficient.

I don't have enough fingers or toes to count the number of botters that have done this without issue.
The other problem with the Y carriage on the prt's was the unistrut is short at both ends which leaves about a 1" gap between it and the square tubing of the y-carriage. Adding an "L" bracket to the inside will increase rigidity and help reduce flex.

Doug I strongly disagree with your comment of "Your gantry is driven from both sides and has no reason to get out of sq."

Just because you have 2 x- motors does not mean it will not get out of square, power down and bump one side of the y carriage, power back up and it will run but be out of square, it may bind if you bump it to much but its doable. One reason you have bump blocks set at the end of the table, to square and realign.

Lets not forget this is a 2000 prt we are discussing here

[joe]

Gary,

These fellows are relative newbees experts. They've not run any other equipment.

SB is a kit. It's bolted together. The only reason is to save money not to improve quality.

Joe Crumley
www.normansignco.com (http://www.normansignco.com)

[garyb]

Good to see you back posting Joe.
Haven't seen you're good sense of humour for a month or so.
Hope everything is going OK & your keeping busy.

[coach]

Actually a tack weld is to hold position while welding. most tacks will have tiny cracks in them or a small pin hole.
For strength a small bead will be the best choice.
Not a large fillet as Gary stated but maybe an inch long.
Just sharing my welding experience. Not suggesting to or not to weld the shopbot.

[roy_shimp]

Chuck - I realized that after i read your post i did't explain why i was thinking about welding. My gantry is out of square about .125". To find this i held a carpenters square to an inside corner of the gantry to see it. Also i have .125" sag in the middle of the gantry where the Colombo carriage rides back and forth.

Gary - i was thinking about what you mentioned,as i do have two bolts at each corner.
"The other problem with the Y carriage on the prt's was the unistrut is short at both ends which leaves about a 1" gap between it and the square tubing of the y-carriage. Adding an "L" bracket to the inside will increase rigidity and help reduce flex".
Also, should i straighten the sagging in the middle of the gantry area by welding the unistrut to the gantry or replace the unistrut and weld something else to the gantry.

Thank you everyone or your ideas. I have had this PRT 4x8 since 2000 and it has done well for me. Roy

[garyb]

Roy I would not weld the unistrut to the frame.
Check where the sagging is actually happening.
Unbolt the unistrut and check if they are bowed, replace if needed. Setting a camber to the unistrut will also correct sag.

The only weld I would do is a tack (3/8" to 1/2" long for all the excited ones)on the angle iron to the square tube of the y carriage, but only after every thing is set, aligned and squared.

[coach]

not excited, welder wannabes shouldn't give technical advice.
trying to return some of what I have taken from this most generous forum.

[garyb]

yeah your right since i did my welding certification at AR tech/Williamstown Naval Shipyard back in '78 and moved on realizing I didn't want to push a stick for the rest of my life I would say that makes me obsolete

[navigator7]

Gary,
That your machine runs square is all that matters.
It cuts a box and not a parallelogram now, right?
Dial indicators are wonderful tools

Consider a turnbuckle or two......and then a tack or a weld???
I don't know anything about your rails.

[garyb]

Chuck this was not about either of my machines they are both fine.
Roy had posted the question about welding a PRT and as I had been through this 4 or 5 times including doing it to one of my own machines had responded.

[navigator7]

Ahhhh!
I meant to write Roy.
First mistake I've made this year!