Steel G0704 base/y saddle

[Upnorth4]

I have been running my CNC G0704 since 2016. It has served me very well. It’s a very basic set up with the stock dovetails and stock y travels.

I’m falling down the rabbit hole on upgrading it. I recently burnt up a dc speed controller for the spindle motor and started to look into a 3phase ac motor. Which has led me to consider cutting off the dovetails and adding linear rails. And if I do that to the Z might as well do it to the X and y. And if I’m doing that then might as well extend the y. And if it do that (which would mean cutting a slot pretty much through it and cut off the dovetails) I might as well just make a new base……


I have access to 2” plate steel, just in 13” round pieces. I’m thinking about cutting the rounds into the pieces and welding them together, then machining those for the linear rail pockets and a slot for the screw/bearing. After machining I’ll pay a shop to surface grind the critical surfaces…


Would welding pieces of 2” plate result in a sturdy enough platform? (I would certainly research best practices for proper weld prep/bevel sizes)

Would it be any less rigid than cutting through the saddle and adding spacers?

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[joeavaerage]

Hi
welding 2 inch thick material is not easy. To get full penetration welds is likely to be really time consuming or something that should be done with sub-arc.
Once you are done you will have to thermal stress relieve or the steel will move every time you touch it. Thermal stress relief requires putting in in an oven
at something like 700C for many hours....its not cheap, and certainly not something you can do yourself.

I think welding is a mistake.

You should get a piece of steel plasma cut. I priced some plasma cut steel plate just a couple of months ago in 32mm medium tensile and found that it works out
to about $6.00NZD/kg ($4.00USD/kg). Thus a piece 200x 600 of 50mm would be about $288NZD ($175USD). If you were to go this way then stress
relief is not required although you would probably still want to grind it. I had three pieces of 375 x375 x20 done for me about a year ago and cost me $90.00NZD ($60.00USD).

Craig

[Upnorth4]

I have a unique position where I can actually heat treat. I have a kiln that I have done 14hr burnouts of lost form molds for casting (it has a ramp controller so annealing I could be done), so if it is that critical I can heat treat the frame after welding. I am also in a unique position where I have access to scrap metal and a large manual knee mill.

I have seen builds where the stock saddle is extended with aluminum blocks and linear rails are bolted on….2” steel welded out and milled after must be more stable than that….

I’m on the verge of just leaving the G0704 mostly alone. Welding together a base and column and adding a machined plate for a saddle, possibly filling the base and column with epoxy granite……
Using the head and spindle for the G0704 would increase the chances of success…..
Just need to source linear bearings and longer screws….

[joeavaerage]

Hi,
well yes having a heat treatment facility is a great bonus. If you attempted to weld 50mm steel you'll need it bigtime.

I'm still of the opinion that getting a piece of steel plasma cut is still the cheapest and most stable way forward.

Craig

[Upnorth4]

I’ll draw it up and get a quote, I’m curious to know what a solid piece cut to shape would cost….

[joeavaerage]

Hi,
I think you'll be pleasantly surprised, plasma cut steel is not cheap....but has consistently surprised me with its price relative to other engineering
materials.

Craig

[maxspongebob]

For what you are talking about doing the amount of work and cost will probably be greater than a new/used mill and it may also turn out to be a bigger problem. There are many aspects of the G0704 that are poorly designed and when you start trying to expand it's envelop it just gets worse.

I think you would be better off just buying a new manual mill and use the 704 to convert it. Also if you can't find a machine base that suites you then build a new machine from EG. When you are finished sell the G0704 and be done with it.

[joeavaerage]

Hi,

Also if you can't find a machine base the suites you then build a new machine from EG.

BS. EG has Youngs modulus of 30-50GPa whereas cast iron is 110GPa and steel 205GPa. If you want a stiff machine you will have to use a lot more
EG than either steel or iron. You have a large mill which can be used on steel and iron but not EG.

Steel, followed by iron, is the lowest cost highest rigidity material out there. Steel is the premier engineering material of humanity, to whit; 1900 million tons of steel
made in 2020. EG....not so much.

Craig

[Upnorth4]

My intent is to build a new base, saddle and possibly column. The column is what would likely be the tipping point of selling the G0704 and hitting auction sites…..
EG would only be cast around the steel frame to increase the mass and reduce possible vibration. This would only be done on the base.

Main driver of doinging any of this is to get rid of the dovetails. The saddle would be easy to machine on the knee mill I have access to, and easily done out of plate. I think it would be easier to make a new saddle than modify the existing casting. As for the base I have seen pictures of other mods that cutoff the dovetails and increase the y travel and there doesn’t look to be much “meat” left. Again a plasma or flame cut 2” plate encased in EG really interests me.
I do think I can pull this off fast that sorting out the hurdles in converting a different manual mill.
I have already converted the spindle and drive. 5000rpm all day without heating up, belt drive, power draw bar AND I get to keep the quill….. It would take a lucky find at an auction to meet all of that and no way would it be cheaper than a set of linear rails and a couple pieces of plate….

[joeavaerage]

Hi,

Again a little plasma or flame cut 2” plate encased in EG really interests me.

Don't worry about the EG. The density of steel is four times that of EG, if you want more weight just use more or thicker steel. There are tens of thousands of machines out there made of steel
and/or iron....do they vibrate like hell....no. You don't need EG.

Craig

[pippin88]

Adding weight (mass) just to add weight is not beneficial. Heavy does not equal stiff.

Increasing stiffness (and having more weight because of increased quantities of appropriately placed material) is beneficial.

I agree with Joe that stiffness is king. I disagree that damping doesn't matter (theme in Joe's posts over many threads). There is plenty of evidence that damping improves surfaces finish. Yes the best first step is a machine as stiff as possible. Ideally so stiff it does not deflect at all, but in reality this is impossible. You will have some vibrations at some point. Steel rings like a bell and keeps ringing. Appropriately designed damping (can be composition materials, particle dampers, constrained layer damping) is helpful.