gadget_lover
Flashaholic
There have been many, many threads about what kind of equipment to buy. Many questions have been asked again and again. Many people have said that benchtop machinery is too flimsy for precise work. The mantra "Mass = rigidity" has been repeated more than once.
Now, I have a micro mill (less than 2 feet tall, 1/5 hp) and a mid sized mill (a touch over 5 foot tall, 1.5 hp) and a mini lathe (under 3 feet long 1/3 hp). I've often said that the bench sized machines were quite capable, and have recommended them often.
But the question has always haunted me; Are the professional machines that much better? I have used the small machines for several years, but had no point of comparison till I bought my big one.
This weekend I answered the question. I spent $60 for a couple of hours with a Bridgeport vertical knee mill and a 12 x 48 Enco lathe at the local Techshop. If you are not familiar with them, Techshop is a membership machine shop with several locations throughout the US. Web page is www.techshop.ws (yes, .ws, not com).
I paid my $60 of my Christmas money for a "basic saftey and use" (BSU) session. Now that I'm "certified" I can drop in any day from 9 am to midnight and use their machines for $50 a day or $125 a month.
The BSU was very basic. We went over the basic controls, the do's and don'ts, and then we each got to play with a machine for a while. I used that time to mill a small block to the same standards as similar ones I'd done at home.
I'd like to share some of my discoveries...
1) The benchtop models and the big boys use exactly the same techniques and follow the same basic rules. This makes sense because they follow the same laws of physics.
2) The biggest difference is simply horsepower. This means the big machines NEED to be stiffer, since they have several horsepower and lots of torque to withstand. The 3 HP motor on the mill provides instant torque that would quickly bend the frame of my 1/5th HP micro mill. The 1/5 HP motor on my micro mill does not stress it's frame at all.
3) The Big machines can be just as inaccurate as the small ones, and for the same reasons. If you do not follow the rules, lock down the axis that is not moving, use sharp tools and pay attention, either will deliver shoddy work.
Now some conclusions;
The stiffness of the machine needs to be directly proportional to the power. The depth of your cuts also have to match. I milled three small parts, one on each machine. All were within the .001 that I wanted them to be. All three had finishes that needed little touchup. My midsized mill left the best finish (smooth as silk) , but I spent the most time adjusting the alignment. The big mill gave the worst finish, but I suspect that it was not trammed (aligned) well. The smallest mill had the fewest points where it could be aligned.
If you adjust your cuts to match the stiffness of the machine, you get equal results with all three. It is FASTER to make parts on the two bigger machines since you can use bigger tools that can cut wider and deeper per pass. If you make more passes you can go just as wide (limited by the table) or deep on the small mill.
A bad idea on a small machine is a bad idea on a big one. The Techshop used R8 collets to hold the endmill, which pulled out as we used it. The cut got dangerously deeper as we traversed the length of the piece we were facing, starting at .015 and dropping down to 1/2 inch before we noticed.
Some folks talk disparagingly of the plastic (phenolic) gears in the benchtop machines. I can see why the big ones would break instantly if they used plastic. The large, single speed 3 phase motors go from zero RPMs to full speed in the blink of an eye. Plastic in the drive train would shatter in no time. The small machines use lots of plastic, but they also frequently have an electronic speed control that provides soft starts. The power is also 1/10th of the big guys, so the stresses are that much lower.
The bigger machines have more room to fit neat stuff. The ENCO 12x48 lathe had lots of extra capabilities that just would not fit on a 3 foot long benchtop unit. The built in coolant pump and motorized carriage travel (infeed as well as Z axis) would be neat, but take a lot of room. I'd kill for the quick change gearbox for threading. The larger tables of the mills make it easy to mount things like DROs', power feeds, lamps and other goodies.
The bigger tables and taller headroom of the bigger mills make it easier to create setups. You can add multiple setup blocks in different combinations to hold the work just so. But the vices, blocks and angle plates are smaller and cheaper for the smaller machines. I'm looking at a 8 inch rotary table for $300 for my bigger mill. The 4 inch rotary table on my micro mill was under $80.
In conclusion, it was nice to see that when working with mild steel or aluminum, my benchtop units compare favorably. Well, they do once you factor in space, power and scaling your cuts to the capabilities of the machines. There are, of course, materials that require deep or aggressive cuts that might not be viable on a benchtop uinit.
Daniel
Now, I have a micro mill (less than 2 feet tall, 1/5 hp) and a mid sized mill (a touch over 5 foot tall, 1.5 hp) and a mini lathe (under 3 feet long 1/3 hp). I've often said that the bench sized machines were quite capable, and have recommended them often.
But the question has always haunted me; Are the professional machines that much better? I have used the small machines for several years, but had no point of comparison till I bought my big one.
This weekend I answered the question. I spent $60 for a couple of hours with a Bridgeport vertical knee mill and a 12 x 48 Enco lathe at the local Techshop. If you are not familiar with them, Techshop is a membership machine shop with several locations throughout the US. Web page is www.techshop.ws (yes, .ws, not com).
I paid my $60 of my Christmas money for a "basic saftey and use" (BSU) session. Now that I'm "certified" I can drop in any day from 9 am to midnight and use their machines for $50 a day or $125 a month.
The BSU was very basic. We went over the basic controls, the do's and don'ts, and then we each got to play with a machine for a while. I used that time to mill a small block to the same standards as similar ones I'd done at home.
I'd like to share some of my discoveries...
1) The benchtop models and the big boys use exactly the same techniques and follow the same basic rules. This makes sense because they follow the same laws of physics.
2) The biggest difference is simply horsepower. This means the big machines NEED to be stiffer, since they have several horsepower and lots of torque to withstand. The 3 HP motor on the mill provides instant torque that would quickly bend the frame of my 1/5th HP micro mill. The 1/5 HP motor on my micro mill does not stress it's frame at all.
3) The Big machines can be just as inaccurate as the small ones, and for the same reasons. If you do not follow the rules, lock down the axis that is not moving, use sharp tools and pay attention, either will deliver shoddy work.
Now some conclusions;
The stiffness of the machine needs to be directly proportional to the power. The depth of your cuts also have to match. I milled three small parts, one on each machine. All were within the .001 that I wanted them to be. All three had finishes that needed little touchup. My midsized mill left the best finish (smooth as silk) , but I spent the most time adjusting the alignment. The big mill gave the worst finish, but I suspect that it was not trammed (aligned) well. The smallest mill had the fewest points where it could be aligned.
If you adjust your cuts to match the stiffness of the machine, you get equal results with all three. It is FASTER to make parts on the two bigger machines since you can use bigger tools that can cut wider and deeper per pass. If you make more passes you can go just as wide (limited by the table) or deep on the small mill.
A bad idea on a small machine is a bad idea on a big one. The Techshop used R8 collets to hold the endmill, which pulled out as we used it. The cut got dangerously deeper as we traversed the length of the piece we were facing, starting at .015 and dropping down to 1/2 inch before we noticed.
Some folks talk disparagingly of the plastic (phenolic) gears in the benchtop machines. I can see why the big ones would break instantly if they used plastic. The large, single speed 3 phase motors go from zero RPMs to full speed in the blink of an eye. Plastic in the drive train would shatter in no time. The small machines use lots of plastic, but they also frequently have an electronic speed control that provides soft starts. The power is also 1/10th of the big guys, so the stresses are that much lower.
The bigger machines have more room to fit neat stuff. The ENCO 12x48 lathe had lots of extra capabilities that just would not fit on a 3 foot long benchtop unit. The built in coolant pump and motorized carriage travel (infeed as well as Z axis) would be neat, but take a lot of room. I'd kill for the quick change gearbox for threading. The larger tables of the mills make it easy to mount things like DROs', power feeds, lamps and other goodies.
The bigger tables and taller headroom of the bigger mills make it easier to create setups. You can add multiple setup blocks in different combinations to hold the work just so. But the vices, blocks and angle plates are smaller and cheaper for the smaller machines. I'm looking at a 8 inch rotary table for $300 for my bigger mill. The 4 inch rotary table on my micro mill was under $80.
In conclusion, it was nice to see that when working with mild steel or aluminum, my benchtop units compare favorably. Well, they do once you factor in space, power and scaling your cuts to the capabilities of the machines. There are, of course, materials that require deep or aggressive cuts that might not be viable on a benchtop uinit.
Daniel
