[ero-jiji]

i have a generic Chinese 2.2kw (~3hp 6-24k rpm) water cooled spindle on my current cnc table that we use for aluminum sign making, and have been throwing around the idea of making a low speed spindle adaptor that is driven by the 2.2, and uses vbelt/timing belt for the rpm reduction. the low speed spindle would be built myself, using a grizzly R8 spindle and bearing assembly, and set up to use the tormach TTS tool holders, and later on a pneumatic cylinder to allow for a tool changer.

the setup would be something like this...
Attachment 208548

under normal use, the 2.2kw spindle would be in the holder by itself.
when the low speed spindle is needed, the main spindle would be slid out and inverted, and reinserted in the outboard position.
the low speed spindle would then be slid into the inboard position, a half inch shaft with a set of v grove or timing style pulleys would be inserted into the collet holder, and the chuck tightened.

before i get started on this, a friend recommended that i register here, and run the idea by people who have alot more experiance with this type of machine than i do.

now that i have explained the setup, these are the questions i have.

1. is there a cost efficent (under $500 usd) low speed spindle alternative?

2. v belt or timing pulley?
v belts would allow some slippage if the tool bound up, but i can easily make any size pulleys i want for the reduction ratio
timing pulleys would eliminate slippage, but are available in limited ratio's

3. what rpm should i be looking for on the low speed spindle to run a small (3 inch) fly cutter on 6065?

4. any suggestions/idea's/alternatives or possible issues i should look into?


*edit: note the machine is 4ft by 4foot, and uses 400w servo's, rack and pinion drive. the machine is home built, tho i am not the original builder, and is framed with heavily gusseted 6inch "H" beam gantry and 4inch "H" beam rails. it is regularly used to cut 2" thick 6065 sheet, with onsrud 1/4 inch cutters. coolant is high pressure flood using 30:1 cooltool mix

*edit2: also forgot to mention i have access to a lathe, but do NOT have access to a conventional mill!

[wizard]

i have a generic Chinese 2.2kw (~3hp 6-24k rpm) water cooled spindle on my current cnc table that we use for aluminum sign making, and have been throwing around the idea of making a low speed spindle adaptor that is driven by the 2.2, and uses vbelt/timing belt for the rpm reduction. the low speed spindle would be built myself, using a grizzly R8 spindle and bearing assembly, and set up to use the tormach TTS tool holders, and later on a pneumatic cylinder to allow for a tool changer.

That doesn't say a lot, there are many R8 spindle assemblies used by Grizzly. Personally I'd look for a used Bridgeport head myself.

the setup would be something like this...
Attachment 208548

under normal use, the 2.2kw spindle would be in the holder by itself.
when the low speed spindle is needed, the main spindle would be slid out and inverted, and reinserted in the outboard position.
the low speed spindle would then be slid into the inboard position, a half inch shaft with a set of v grove or timing style pulleys would be inserted into the collet holder, and the chuck tightened.

I'm not sure you would get enough of a reduction in a single stage belt drive to get to a decent power point.

before i get started on this, a friend recommended that i register here, and run the idea by people who have alot more experiance with this type of machine than i do.

Not a bad idea at all. The problem I have with this idea is will you be able to make use of such a low speed spindle in this machine. I really don't know the answer to that one.

now that i have explained the setup, these are the questions i have.

1. is there a cost efficent (under $500 usd) low speed spindle alternative?

Beyond the used market not really.

2. v belt or timing pulley?
v belts would allow some slippage if the tool bound up, but i can easily make any size pulleys i want for the reduction ratio
timing pulleys would eliminate slippage, but are available in limited ratio's

How about neither. First the idea that V-Belts, properly adjust V-Belts, will slip before damage occurs is bogus. It is possible no doubt but it is also possible for the belts to wedge and hold the full stall torque of the motor. I wouldn't do timing belts either. I'd suggest that your best option would be something like a Poly-V belt.

3. what rpm should i be looking for on the low speed spindle to run a small (3 inch) fly cutter on 6065?

I can't say as I've never been near 6065. Beyond that though you should calculate the acceptable surface speeds for various tool to get to the ball park RPM.

4. any suggestions/idea's/alternatives or possible issues i should look into?

Buy tooling that fits into the power and RPM range of your current spindle. Consider balanced shell mills and the like.

*edit: note the machine is 4ft by 4foot, and uses 400w servo's, rack and pinion drive. the machine is home built, tho i am not the original builder, and is framed with heavily gusseted 6inch "H" beam gantry and 4inch "H" beam rails. it is regularly used to cut 2" thick 6065 sheet, with onsrud 1/4 inch cutters. coolant is high pressure flood using 30:1 cooltool mix

*edit2: also forgot to mention i have access to a lathe, but do NOT have access to a conventional mill!

Without access to machinery a custom machine like this gets expensive fast. That is one reason I mentioned a Bridgeport head. Actually any head similar in concept would work. What is needed is a head with a flange that allows easy mounting. Many mill heads would be difficult to use to say the least.

Still I wouldn't consider a low speed spindle until I exhausted every possible way to leverage the current spindle. This is aluminum there should be plenty of tooling out there that can be used in the maximum power range of this spindle.

[rowbare]

Tormach sells their spindle cartridges seperately: 30306 - R8 Spindle Cartridge Assembly this is the R8 for the PCNC 1100. They also have a BT30 version and if you call them, you can probably get the PCNC 770 cartridge. They also sell the complete heads for the mills. They used to list them online before they redid the site. They were in the $1000-$1200 range if I recall.

bob

[ero-jiji]

@wizard thanks for the input, to clarify, the spindle assembly i am looking at is the one for the 1006/1007 2hp mill Grizzly.com
i can purchase the entire assembled quill for roughly $300 P1006316A QUILL ASSY and would simply need to bore a hole in the mounting block to match the outside diameter.

i really like the idea of the multi-v/poly-v belt, and will look into what ratio's are available this weekend.

i had already looked into getting shell cutters for the existing spindle, but the need for a maximum shaft size of 1/2" and minimum rpm 6000 makes for a very limited cost prohibitive selection. currently we outsource the surface finishing on our signs, or use pre surfaced sheets (which are the costs we are trying to reduce).fly cutters are extremely unbalanced, and i wouldn't want to go near one running 1000rpm, let alone 6000, not to mention it would probably shake the machine apart.

i am simply trying to avoid a dedicated machine to do the finishing. i can also use a standard 220v 2hp electric motor which i can source locally to get the unreduced drive speed down to ~3200rpm, with a 5:1 pulley setup that would put my spindle speed at 640rpm (the ideal speed for a 6 inch shell is around 700rpm and 65inches/min in aluminum if i am doing my math right)

[wizard]

I see his biggest problem being the $500 range he is trying to limit this improvement to. There are lots of options out there but even used block spindles are expensive. Add on the need to contract out some parts and the $500 price becomes very difficult to meet.

The other issue which is far harder to deal with, is the machine itself. Would it be stiff enough to realistically make use of such a spindle? They call the machines routers for a reason, I'm not to certain how much conventional milling one could get away with.

Tormach sells their spindle cartridges seperately: 30306 - R8 Spindle Cartridge Assembly this is the R8 for the PCNC 1100. They also have a BT30 version and if you call them, you can probably get the PCNC 770 cartridge. They also sell the complete heads for the mills. They used to list them online before they redid the site. They were in the $1000-$1200 range if I recall.

bob

[ero-jiji]

somehow got double posted

[wizard]

@wizard thanks for the input, to clarify, the spindle assembly i am looking at is the one for the 1006/1007 2hp mill Grizzly.com
i can purchase the entire assembled quill for roughly $300 P1006316A QUILL ASSY and would simply need to bore a hole in the mounting block to match the outside diameter.

In the end you will be well over your $500 mark. Plus building a mounting block with motor support will be non trivial. I'd seriously consider looking for a used Gilman or other spindle assembly.

i really like the idea of the multi-v/poly-v belt, and will look into what ratio's are available this weekend.

Actually any ratio you could imagine if you DIY the pulleys. Well within the recommended ratios and belt wraps.

i had already looked into getting shell cutters for the existing spindle, but the need for a maximum shaft size of 1/2" and minimum rpm 6000 makes for a very limited cost prohibitive selection. currently we outsource the surface finishing on our signs, or use pre surfaced sheets (which are the costs we are trying to reduce).fly cutters are extremely unbalanced, and i wouldn't want to go near one running 1000rpm, let alone 6000, not to mention it would probably shake the machine apart.

Fly cutters are regularly ran above 1000 RPM even when cutting steel. In fact given the right material, motor and cutters you could run right off a 1700 RPM motor. It wouldn't be a standard motor due to excessive axial end play common in motors but the point remains speed isn't an issue given that the cutters can handle it.

i am simply trying to avoid a dedicated machine to do the finishing. i can also use a standard 220v 2hp electric motor which i can source locally to get the unreduced drive speed down to ~3200rpm, with a 5:1 pulley setup that would put my spindle speed at 640rpm (the ideal speed for a 6 inch shell is around 700rpm and 65inches/min in aluminum if i am doing my math right)

Yeah I have a few problems here. First and foremost we are talking about a router type machine here. Now there is almost an infinite number of designs out there, so the question that comes to mind is how do you know if your machine will even handle a six inch fly cutter? Will it maintain tram, under load, running a cutter with that radius? Will you be able to setup the spindle assembly in a repeatable manner so again the spindle is properly trammed to the work table?

These guys have some interesting stuff on fly cutting: Feeds and Speeds for Fly Cutters and Manual Mills. Follow some of the links. I do think you might want to look here and at other resources on the web to get a better idea as to what is involved here.

In any event have you considered replacing the primary spindle with one that produces good torque in the 2000 RPM range? I realize that you need the faster RPMs to do the other work but it might make life easier to just look for a spindle that can get you down to to 2000RPM range. Run a much smaller fly cutter at this speed with the right inserts so that you get the surface finish you are after. 2000 RPM may sound like a lot and in a way it is for a big diameter cutter, but let's say for sake of argument you make a 1" diameter cutter, that might be seen as low speed then. I used one inch here due to you stated half inch shank size in the current spindle. You can mess around here with sizes for a single tip cutter, you might even find a solution that works at 6000 RPM. Now if you say you machine isn't stiff enough or aligned accurately enough to run the smaller cutters I have to seriously think about the viability of a 6" cutter.

By the way surface finish will vary dramatically with the alloy you are machining.

In any event I have to wonder what you have attempted to run so far on the machine single point cutter wise. Noticed I said single point cutter, because not every single point cutter looks like a massively unbalanced fly cutter. In the end I'd try to get the current spindle to work with something or try to find a spindle with a wider speed range to replace the current one first. I just see swapping spindles back and forth as being difficult.

[ero-jiji]

i was unaware that a fly cutter could be spun that fast safely, looks like i need to do a bit more research before i proceed on this.

as for the stiffness of the machine, im pretty sire its a non issue, the gantry itself is used to lift and load full 4x8 sheets of 2" thick 6065 via 2 vacuum plates mounted to air pistons directly attached to the gantry, and altho i havent put a dial indicator on the beam to measure deflection when loading, the machine has been used in its current current setup since i bought the business about 8 years ago with no issues. ill get some pictures when i go in to work on monday and post them to give you a better idea of the machine.

im really glad i did the post here before just jumping into the project, your insight has been invaluable wizard!