[etard]

Hypothetically, if one were to be able to purchase a quality surface grinder for a decent price with say 8" y axis travel and about 15" in the x, what problems might this person encounter in converting this to a full on bed milling machine?

I could pick a decent one up for close to a grand but I have never seen one in action. Can anyone verify the rigidity of these machines? Any possibility of putting a 3KW spindle on the z movement and still be sturdy?

[jeffery926]

I would not recommend it.

Surface grinders are designed to be very precise, but will not take heavy machining loads like a milling machine will. Grinding is normally only done a few thousands at a time per pass. Can you make it rigid enough? Possibly by doing some serious modifications to the machine. I had a KO-Lee surface grinder and the bed floated on oil pumped between the ways and driven by a rack and pinion, but just held down by the weight of the bed itself. I have setup a horizontal milling machine do surface grinding fairly easy though.

[RICHARD ZASTROW]

Why not just buy a mill for close to a grand?????

Dick Z

[etard]

Calm down dude, I'm just trying to think outside the box. At this price point, the comparable mill would probably be the infamous G0704. I'm not completely sold on the merits of that machine, especially with all the half assed machines out there with half ground precision surfaces.

[wizard]

Hypothetically, if one were to be able to purchase a quality surface grinder for a decent price with say 8" y axis travel and about 15" in the x, what problems might this person encounter in converting this to a full on bed milling machine?

The general arraignment of most grinders is table that sits on top of some ways. Often V ways combined with flat ways. There is nothing clamping or retaining the table on those ways. This immediately limits any mill conversion to those techniques that don't put lifting torque on the table. Basically what you have is a planer mill after a simple conversion.

I could pick a decent one up for close to a grand but I have never seen one in action. Can anyone verify the rigidity of these machines?

Actually a grinder has to be pretty rigid for its size. The forces are such that the wheel pushes down on the table and up on the spindle so the columns are optimized for that sort of loading.

Any possibility of putting a 3KW spindle on the z movement and still be sturdy?

That would depend upon the grinder, the orientation of the spindle and other factors.

Honestly I wouldn't bother with most grinders. If you got one dirt cheap that would be one thing, like a $100 bucks or so. There might be a greater pay off if you found a machine where both sets of ways where flat and you could easily mount linear bearings to the table and frame. Another issue you might run into is where to put the lead screw, the drive mechanism on a surface grinders table can be anything from a rack, to a steel cable to a timing belt. This means there might not be clearance for a lead screw.

In the end this probably isn't something to even bother with unless you already have a machine shop and also have a specific need for some sort of horizontal milling. Even then you ought to consider searching for horizontal used mills.

[wizard]

Calm down dude,

Calm down. --- what is that nonsense all about. You continue to give people grief like that and help will go out the window!

I'm just trying to think outside the box.

There is nothing wrong with that, that is where innovation comes from. I just don't see it as a viable project in most cases. Frankly it would be more work than buying an old used Bridgeport and rebuilding it.

At this price point, the comparable mill would probably be the infamous G0704. I'm not completely sold on the merits of that machine, especially with all the half assed machines out there with half ground precision surfaces.

Actually I agree with you to an extent, the product being shipped lately seems to be burning a hole in any positive reputation the G0704 ever had. That sucks really because the design is nice. However if you are willing to expend a great deal of time and effort on a surface grinder conversion that will have issues no matter what you do, why not consider putting the effort into correcting whatever issues a delivered G0704 may have? The G0704 is a known gamble at this point where as a surface grinder conversion would cost you a lot of money on top of the cost of the base machine. More importantly that would still be an iffy surface grinder conversion.

Your concerns about the G0704, or any low cost Chinese machine for that matter, are real but your only real options at these price points are used manual machines or possibly a used CNC machine with a crapped out controller. Those used machine can range from like new to totally in need of a rebuild. So you are still in a position of throwing cash into a machine to bring it up to good condition. With the Chinese machines you know up front that you will need a new spindle motor sooner or later, with a used mill that USA made motor from 1950 could go to hell in a week or two decades later. The fact of the matter is good quality machinery costs a lot of money even if it is made in Asia. So if like most of us your budget is limited, the only choice you have is to gamble a bit and be prepared to put effort and $$$$ into the machine.

[etard]

Wizard,

I may not always like your answers, but I sure do appreciate your input!

Good to hear about the rigidity of the spindle, I was actually thinking a ram sturdily mounted through the z position carrier and attach the spindle Bridgeport style.

The reason Dick Z got my panties in a bunch is that his reply was completely counter-productive and also because the level of used surface grinder far surpasses the China mill (x2) that can be had for a similar price. Am I wrong?

[neilw20]

The only thing holding the bed down on my grinder is gravity and the end covers.
Take off the end covers and the bed lifts off.
Say you were drilling a hole, and the thing feeds up the drill, then the table will lift.
Using it for engraving, though would be great or using tiny cutters that can't lift the table,
after you figure how to drive the table, of which mine is rack driven.
My Z ways on the grinder need linear guides now as the Z dovetail is just to crappy to be worth a refit.
Best thing I did to the little grinder is a add a VFD so you can grind stuff that typically melts.

[wizard]

Wizard,

I may not always like your answers, but I sure do appreciate your input!

Sometimes I don't like my answers myself, working 12 hours shifts an do that to you😬.

Good to hear about the rigidity of the spindle, I was actually thinking a ram sturdily mounted through the z position carrier and attach the spindle Bridgeport style.

I'm still of the opinion it isn't worth pursuing unless you can get much of the hardware extremely discounted. Even then you would be very limited as to what you can accomplish on the conversion. I still think a horizontal conversion is the only thing that makes sense and still you would have a limited machine.

There has been lots of talk about the issues with the table and cross slides ( nothing to hold them down) which you can't dismiss but you also have to consider the forces a grinder doesn't normally sees. By the time you address all of these things you will have spent a considerable amount of time and money. Seriously you could get some wood and some hand tools and build patterns for a machine built from new castings and probably spend less time and even less money. I

The reason Dick Z got my panties in a bunch is that his reply was completely counter-productive and also because the level of used surface grinder far surpasses the China mill (x2) that can be had for a similar price. Am I wrong?

Honestly I think you are wrong.

First not every surface grinder is designed the same way. In some cases I can't see a reasonable conversion being done. The other thing is that I think you are dismissing the expense here. Yes a conversion of a Chinese mill costs $$ too but you get (in most cases) a functional machine out of the box. A grinder conversion is a very long ways from being a usable machine no matter what the level of conversion you do. On top of that you need a machine shop to do a grinder conversion in the first place.

Don't dismiss the idea though just realize it isn't the cheapest nor easiest way to get to a vertical CNC machine. No matter how bad the Chinese mill will be out of the box, getting up and running will be far easier. By the time you have addressed a grinders short comings, the ways and saddles with linear slides for example, you will have spent a lot of money and you still have other things to deal with. Consider for example that most grinder tables leave a lot to be desired as vertical mill tables. You might only have one Tee slot on a grinder table.

[wizard]

The only thing holding the bed down on my grinder is gravity and the end covers.
Take off the end covers and the bed lifts off.
Say you were drilling a hole, and the thing feeds up the drill, then the table will lift.

Depending upon the grinder the saddle has the same problem. Unless you address this issue I only see such a conversion as useful if the machining is done like a grinder using horizontal mill techniques.

Using it for engraving, though would be great or using tiny cutters that can't lift the table,

The problem is once you have a mill you will want to do many interesting things on it.

after you figure how to drive the table, of which mine is rack driven.
My Z ways on the grinder need linear guides now as the Z dovetail is just to crappy to be worth a refit.
Best thing I did to the little grinder is a add a VFD so you can grind stuff that typically melts.

[etard]

Well, you have me convinced, I didn't realize the surface grinders were built in such a way. I will have to look at one some day. I actually already have a Diamond horizontal mill ATM, and I don't want to be the first guy to CNC one either! Lol.

[Jos55efina]

I actually already have a Diamond horizontal mill ATM,