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04-04-2006, 11:32 PM #1
I'm sure this topic has been flogged to death and back. I'm wondering about the pros and cons and differences between gearhead and belt drive mills? Of course there's the obvious things like broken gears vs. a slipping belt, and it's easier to change gears than to hustle the belts from sheave to sheave. I've heard that the belt drive are quieter than the gears. How much quieter? I read that the belt drive machines leave a smoother finish on parts than the gears. Something about vibration being transfered to the quill. Fact/fiction? Anything else I missed?
This is the machine I am thinking about buying for my hobby shop.
04-05-2006, 03:06 AM #2
I have a similar square column mill drill -- and am not much impressed with the change gear mechanism. The detents didn't match the gear position. Overall, a good value for the money, but the same mill with a belt drive would probably hold up longer in service.
04-05-2006, 10:51 AM #3
Is the gear train typically a cheaper/weaker setup than belts and pulleys?
04-05-2006, 11:19 AM #4
I talked to a couple of guys who installed VFD's.
A major improvement to the machine.
I'm considering, would fit my needs.
04-05-2006, 06:29 PM #5
I'm too new in this game to have much more than an opinion based on other's opinions, but I'm pretty much sold on a belt drive and 3 phase with VFD for lathe or mill.
I'm currently running my 2J varidrive 1.5hp Bridgeport on a VFD and it is absolutely amazing. I also have a small belt drive lathe that I am either converting to 3 phase or replacing with a larger one, either way, 3 phase. With the mill having the varidrive, the VFD is not such a big deal, but on a lathe, particularly for threading, it would be just the thing to get down to 30 rpms or so as needed without all the belt switching, assuming motor hp and design allow (inverter duty, vectorless support, external fan perhaps, that sort of thing).
All that said, the VFD removes (IMO) the only win for gear drive, and that is easy/fast speed changes. I've been present and used gear drive machines of a few sorts and for the most part they seem much "rougher" and noisier, as well as the reported potential lack of longevity. The belt machines are SO much smoother and quieter, and I'm told that this can show up in the work in some cases too. And the gear train negatives seem by far most pronounced in the low end import machines.
Belt systems are also simpler to maintain, fix, or even modify within reason (for instance, add a jack shaft or something).
So for me, belts and VFD is the only answer. The only time I have to listen to gears is when using the back gear for torque multiplication on mill or lathe, or the feed/thread gears...
04-05-2006, 06:36 PM #6
Allan -- a gearhead is typically more expensive, more convenient, and able to transmit more power. My point about the gearing on the Chinese square column mill drills -- at least my Lathemaster unit -- is that they've done it on the cheap, it takes more fiddling to engage gears than it should, and if they aren't engaged properly reliability will suffer (not full width contact on the already narrow gears). It's still a good value for the money, but I would have preferred a belt drive square column machine built to a higher standard. To my knowledge, that doesn't exist in any of the imports.
The Grizzly is a 3 phase machine -- and a VFD would be the way to go if you have only single phase. You should still use the change gears to get max torque, but will find a lower low end and a higher high end to be of use sometimes. A genuine Rong Fu (Taiwan) may be built to a higher standard -- but is several hundred more.
04-05-2006, 07:36 PM #7
We have the Grizzly machine at work running production drilling holes using a jig and countersinking and counterboring operations. It is a few years old now and no problems. It gets run in faster gears in drilling and slower gears when countersinking. The bevel gears on the column hand crank needed shim washers to bring them into tighter mesh, but that's minor. I have fitted the machine with two hand controls and an air operated automaitc clamping jig. It is holding up well for all the use it sees. I also set one up like this and sent it to out China factory. Full circle iron irony, eh?
PS- Automationdirect.com has GS1 vfd's for a little more than $100.
04-05-2006, 07:38 PM #8
I have cnc both gear head lathes and mill and belt slappers...... belt is the only way to go.
EVERY cheap gear head machine I have had blow the gears in less than a year. my vote is 100% for belts.
04-05-2006, 08:26 PM #9
It's one of those professional verses hobby things. Belts are quieter cheaper and ok for home and bespoke use. But quick change gears are good for production use - more productivity.
Oh and if the table is driven of the same drive the belt slip variation can cause variation in cutting speeds - so can be uneven and you may not be able to be so agressive in the cut rate.
So if you can afford to be gentle and take a bit longer go belts. If money making go gears. Actually for comercial, I would go all out for a full on CNC machine.
04-05-2006, 11:26 PM #10
Thanks for the great info guys. Now my next question. Given a choice, would you choose the gear-head mill/drill, or a 6X26 import knee mill?
04-06-2006, 08:54 AM #11
That china gearhead mill is available in round and dovetail column. The dovetail column I think is just as good as a knee. I think you could call it a bed mill, not sure. What you are after, is the tool stays alligned in the X-Y postiton when the Z is changed. This is a problem with a round column mill, but dovetail column or knee eliminates this.
04-06-2006, 02:28 PM #12
Maybe a little background might help here. I build model steam engines and do a little bit of gunsmithing. I do small amounts of commercial work too. I machine aluminum, brass, and mild steel. I mostly use end mills in the 1/8-1/2" range. I'm moving up from an X2 minimill. I'm sure I don't want a round column mill/drill as the loss of registration when I raise and lower the column would drive me crazy. Given what I want to do with the mill, would I be happier with the gearhead dovetail mill, or the 6X26 knee mill? Or is there an even better choice in new mills? Size is always a factor too, as I need to move it into a home garage.
04-06-2006, 02:47 PM #13
Before I found my Bpt, I was about to give up and get an import (glad I didn't, but that's a different point). At the time, I was looking at the mini Clausing and Bridgeport knee mills. I preferred the knee to the square column due to the way it seems to work with respect to milling forces. Any slide must, by definition, have some clearance. This clearance can lead to chatter and finish problems depending on severity and how it comes into play. When a work piece is on the table, the forces of the piece and the table is downward due to gravity. The cutter is adding down force (plunge) and/or side force. Even when cutting sideways, there is generally a significant vertical component pushing the head and table/part away from each other. In a knee config, all the downward forces are naturally taking out any slop (left by the locks or sliding way) and any forces “up” are very minor in comparison to the summed down forces. And most everything on the top side of the cut is rigidly (relatively) set solid and cinched up except for the spindle/quill. But consider a square column. That vertical way that is held tight by weight combined with lots of mass/inertia on a knee config now only has the head hanging off, and again, the weight is pulling out any slack in a downward direction. But the cutter applies forces upward (in general) so any slack at all is going to show up quickly as the weight of the head is countered by the up force from cutting. Not to mention the column seems less rigid than a typical knee column. When knew, this may not be a big problem, but it seems this balancing of forces would amplify any problems due to wear (or cheap ChiCom fit). The down side of the knee mills is that the square columns typically have a fair bit more z-space to work with and they cost more for comparable work envelope.
For what you do, will any of this matter? Probably not, I know a lot of folks doing the same thing (even with a round column HF!) that are successful and happy. I'm doing bigger automotive (mostly 4x4) type stuff and it seemed important for me...
04-06-2006, 04:57 PM #14
I would go with the "bed mill" style "mill-drill" instead of the small knee mill (the overall build on the small knee mill is kinda light). A large knee mill (like BadDog's Bridgeport) vs. the mill-drill however would be a diffrent story. And for your use, I don't think that the gear head is going to cause you much trouble.
>> Even when cutting sideways, there is generally a significant vertical component pushing the head and table/part away from each other.
That depends on the cutter, material, feed, and speed. Sometimes it can go the other way - the forces end up pulling the cutter into the part -- so no matter what, check that your locks and collets are good and tight!
04-06-2006, 06:06 PM #15
Thats why I said "generally" and should have added "for what I'm doing" too I guess. Still lots to learn, but those were my thoughts at the point it became irrelevant.
But thanks for the correction. Best thing about these forums is I can air my thoughts and understandings (or misunderstandings as it may be) without worry about leading someone wrong. And when I have it wrong, I can quickly eliminate my mistakes and misconceptions before they cause me too much damage.
04-07-2006, 10:05 AM #16
Great advice. Thanks for all the responses. This metalworking stuff is slowing starting to sink in.
08-11-2006, 02:31 PM #17
I have seen both mills in the real world and worked on one similar to the G0519. Concerning size, they both are monsters. The G0519 is not far from a bridgeport in footprint (table size is the word here). Go to an outlet and take a look, this dampens the shock the day the machine arrives.
Please think about the maximum size of work you want to do before you decide. The working envelope is bigger on the G0519, the manipulations that can be done are nearly the same (x and y travel, swivel head left and right, but the G0519 can´t rotate around the column). Another point is x-y- table size, consider a rotary table with 200mm dia, you´ll need that! Otherwise, clamping the bigger parts is no fun at all.
However, the gear is a big time saver. You don´t even need a VFD( but it´s more convenient), you can also go with a tapped winding motor. This enables speeds up to 2500RPM (with full motor torque).
Then, the quill travel is longer on the G0519. This is nice for deep holes in angular drilling operations ...or cutters with differing length (read again and think, this is very important!). Or concentric drilling operations to the same center, like valves and valve guides in one setup. They´ll never be okay if you have to do it in two steps. Concentric drilling is mandatory here. No need to touch the machines head, on the G0519.
Another thought for a round column mill drill: It´s no problem to attach a keystock precision square rail to the z-column and machine a cutout slot in the head that can use a gib. I´ve seen this on different emco FB mills. This denies rotation of the head while altering z-position.
But this still leaves you with the problem that the angle of the z-axis ist fixed to the table, which is a pain in the back in case you have to make more than one angular drilling operation in a precise manner.
Not to mention that there are models similar to the G0519 that allow you to turn the table sidewards by up to 40 degrees. It´s a nice machine.
Also, it´s easy to cnc it.
Before shopping, put both catalogs side to side and compare and imagine which part can rotate or move in which plane and what it means to machining. Also, take a few difficult parts from the mini mill and try to imagine how attach and run them on your favorite new mill.
Ps.: I lean towards the G0519, because I´m familiar with this machine.
I have not worked with a 6x26, but I know a very satisfied owner.
I guess both are good machines.
08-11-2006, 09:49 PM #18
Johan makes some excellent points. The vertical work clearance on the 0519 Griz is over 18", where it is less than 13" on the 6-26. I have a Van Norman 12, no quill with a vertical clearance of 12" and this is a PITA for drilling and milling with larger endmills. A vise will chew up 4" vertically, a drill chuck (3/8") at least 3" and drill bit extends out 3-4" This leaves precious little space for the work. Rotary table ditto, 2.5-3" tall. Forget about a 1/2" chuck in the 6-26. One way around this of course is a spacer, a 3-6" spacer under the head will solve this problem, and this was a standard option when Rockwell and Clausing originally designed the 6x26 machine, not very hard to make.
One aspect of the 0519, operated on 1ph with a VFD is that the tapping function makes use of the instant reverse a 3ph motor can do, but a VFD can not and you will want to use very high quality taps and lots of lube if you sub a VFD, plus you may have to rewire the switching to control the VFD and not the motor. VFD don't do the 'plug' reverse but ramp down and back up again over at least 1/2sec each way so the tap is going to coast a bit in before coming back out. Others have rewired the 0519 successfully so it taps ok on VFD controls but you need to be aware of this aspect of the tapping mechanism if that is important.
08-12-2006, 12:10 AM #19
For fine, precision work there is no substitute for a bet drive. That is why jig borers are belt driven. Gear-drive works fine for a large production machine where they take huge cuts. As for the G0519 Mill I bought one some time ago as a backup and got rid of it after a few days. It is hopeless. Do not buy it! For example the column on my machine was over .003” out of square – front to back, among a myriad of other problems.
08-12-2006, 12:10 AM #20
Thanks for the feedback guys.
I've narrowed my search to this 8X30 knee mill...
This is apparently the same as the discontinued Grizzly G1008 which I've read good things about.
Or this gear head unit...
Which looks like it has similar specs to the G0519.
The only drawback to the 8X30 knee mill is that the X travel is only 16" vs. the 21" travel of the gear head. I don't need that much travel, at least not yet. You know how that goes. You always need 1/2" more travel than you have now, and wish you'd bought a bigger machine.