G0619 vs G0704 for CNC

[fi man]

Alrighty,

Time to stir the pot!

I've done a fair amount of searching and haven't found any fairly recent dialogues regarding the subject matter. My apologies if I missed the nugget(s).

Disregarding the cost of the mill, which would provide a better CNC foundation - G0619 or G0704?

I acquired a G0619 before the G0704's started to get recognition. Now it's time for CNC. Not wanting to loose my manual milling capability, I have a G0704 arriving shortly.

The plan has been to CNC the G0619, but I had to get curious about the G0704. It seems Hoss originally endorsed the '704 as being a more rigid machine despite a 100 lb difference in weight. I haven't found where anyone ever came to the '619's side in this matter, so perhaps a bit of a one sided argument?

Anyhow, some time has passed for more pro's & con's to be identified regarding these two machines, so I'd like to hear from experiences of both sides of the fence before I commit to my course and order ball screws. Aside from the cost of the base mill itself, the cost of CNCing appears to be about the same using a G540 based stepper system.

So now that some learning time has passed, which seems to be the preferred foundation and why?

TIA

rrr

 

[kd4gij]

Hosses findings can't realy be disputed as he and outhers have bouth and tested side by side. If you read through cnczone you will find most everybody agreas with him. The G0704 is the most populer mill on that site. That said I have no experince with the G0619 but I love my G0704.

 

[jumps4]

I have converted the next size smaller than the g0619 and just finished a g0704 and there is a big difference in rigidity. notice the head mount to column there is a big difference in size and length. for the money the g0704 is a great mill to cnc for light work and the one I did was very well made.
steve

 

[fi man]

Thanks for the replies guys.

I'm not trying to start any bashing, but, I'm going to look at it from an engineering perspective(cause that's what I do! ). I haven't seen that done yet.

I modeled my G0619 a couple of years ago in Solidworks. By assigning material properties (cast iron) I can get weights for base, saddle, column. Didn't model the head, but can wag weights for lead screws, handles, etc, deduct all from published weight and get approximate head weight. I know the distance for center of head to column. Do the same for G0704. While I have the G0704 apart for cleaning, I'll try to weigh on car scales and see how close modeling results are.

Then I'll perform some cross sectional analysis on the square columns of each for bending properties. Can also add the bending load from the head to determine static column flex. It'll be interesting to see what the results are.

Got any links for head to head comparisons of CNC'd units? Things like axis travels are not factors for this kind of comparison.

May even get FEA buddies at work to do deformation analysis of bolting configurations (vertical vs horizontal). G0619 column mounting bolts are primarily under tensile loading. G0704 column mounting bolts appear to be more a combination of both shear loading and tensile loading. The deformation analysis will include flexing of the bases (which may be more significant than the bolts). Don't have any personal experience to make a intuitive call on performance differences in bolting schemes (I'm a mechanical engineer with heavy industrial equipment experience - a few thousandths of flex "ain't nuthin' " ).

Also from posts I've skimmed, seems like the motor in the G0704 is a weak link in the unit. Just an impression I got.

Stay tuned...

rrr

 

[fi man]

G0704 arrived today. Broke spindle in tonite.

Also found some OPTi BF 20 CAD Files tonite, so did some quick column analysis.

G0704 Column
Weight: 46.1 lbs
Ix (Front to Back): 8.224 in^4
Iy (Side to Side): 14.828 in^4

G0619 Column
Weight: 58.1 lbs
Ix (Front to Back): 10.65 in^4
Iy (Side to Side): 26.91 in^4

G0619 column is stiffer in bending Front to Back, but not by much. It is quite a bit stiffer Side to Side, which will also make it stiffer regarding twisting.

On a side note, the base I received had good looking packaging. When I opened it, the top, front ledge was smashed down where something got dropped on it. The mill appears fine so far. Will start cleaning in the a.m.