[skray775]

Here is a rough drawing of the top plate and pulleys'. Excuse the drawing I am not a 3d master! LOL

With the ratios as drawn I would have a 1:1 and 1:1.8.

2HP 3 phase motor.

3" SPINDLE - 3" MOTOR = 1.0 DRIVE RATIO = 1725 RPM
WITH A BELT LENGTH OF 20.16"
@ 50% under speed I would have = 862 RPM
@ 50% over speed I would have = 2587 RPM

2.5" SPINDLE - 4.5" MOTOR = 1.8 DRIVE RATIO = 3107 RPM
WITH A BELT LENGTH OF 21.9"
@ 50% under speed I would have = 1553 RPM
@ 50% over speed I would have = 4660 RPM

I am not that up to speed on VFD so I used a conservative number of 50%.

I am fine with those numbers so if 50% is to low everything above 4660 would be a bonus.

[pete from TN]

Try to make the pulley diameters as large as possible so the belt has the most purchase on the pulley at any one time. That way you can transmit the most power and torque from the motor. Other than that I think it looks pretty good. Personally while I can see the simplicity of using setscrews or whatever to secure the pulley to the spindle shaft using a coupler makes it a simple effort to remove and service the spindle as well as making it also simple to adapt an INTERNAL high speed spindle in the bore such as a pneumatic or electronic spindle. Just a thought.... Good luck with that bad boy!! Peace

Pete

[jid2]

Don't you need some low speed also? I know that I like to do stuff in stainless and you need something around or below 200 RPM it seems like.

[gd.marsh]

I went with 1:2 & 2:1 ratios .. That way you have the exact same belt length so very little motor movement is required to switch.
I also used a 2hp 3ph 1725 rpm motor like you, and I changed out the bearings in the spindle to MUCH higher quality A/C bearings.

At 2:1 (motor to spindle) ratio I get down to 280 rpm with pretty good torque & at the 1:2 ratio I get up to 8000 rpm.
I believe that's running the VFD from 20hz to 130hz if I remember correctly.
If you think about it the motor is only turning at 4000 rpm to produce 8000 at the spindle that way. Standard motor bearings are good to 5500 rpm.
I've been told by motor repair guys that in these general use low hp motors they all have the same bearings regardless of whether their rated at 1725 or 3450.

I just ran a part today using 1/8" ball endmill & the machine cruised along at 8000 rpm for several hours.
Spindle, Motor, & VFD were hardly warm to the touch when done.

[skray775]

Recalculated with the same size pulleys on both ends.

4.5" SPINDLE - 2.5" MOTOR = 0.555 DRIVE RATIO = 957 RPM
WITH A BELT LENGTH OF 20.16"
@ 50% under speed I would have = 478 RPM
@ 50% over speed I would have = 1435 RPM

2.5" SPINDLE - 4.5" MOTOR = 1.8 DRIVE RATIO = 3107 RPM
WITH A BELT LENGTH OF 21.9"
@ 50% under speed I would have = 1553 RPM
@ 50% over speed I would have = 4660 RPM

Pete,
Not sure how to keep the spindle so it can slide out quickly if I use a air cylinder type power draw bar. The cylinder pushes down on the draw bar nut but from my understanding you need some type of flange for the air cylinder mount to pull up against so it does not smash down the spindle bearings.

The spindle has tapered roller bearings so I am not sure if they can withstand the 2500 pounds of force needed from the air cylinder? If they could it would greatly simplify the design but my gut feeling it they can't.

My idea is to use the pulley as that flange. The mounting plate for the air cylinder would be something like the Tormach one pictured. Imagine the black plate under the pulley and the top of the air cylinder over the draw bar nut. When engaged it would pull up on the underside of the pulley and push down on the nut.

I will be drawing it up but I need to gather the dimensions of all the parts first.

[gd.marsh]

Please help me understand why matching pulleys require a different belt length? Or is your last post a typo?

[SCzEngrgGroup]

Recalculated with the same size pulleys on both ends.

4.5" SPINDLE - 2.5" MOTOR = 0.555 DRIVE RATIO = 957 RPM
WITH A BELT LENGTH OF 20.16"
@ 50% under speed I would have = 478 RPM
@ 50% over speed I would have = 1435 RPM

2.5" SPINDLE - 4.5" MOTOR = 1.8 DRIVE RATIO = 3107 RPM
WITH A BELT LENGTH OF 21.9"
@ 50% under speed I would have = 1553 RPM
@ 50% over speed I would have = 4660 RPM

You're doing something wrong in your calculations. If you're swapping pulleys between the motor and spindle, the belt length will be identical in either configuration.

Regards,
Ray L.

[asuratman]

I think the calculation are right, since he did not calc belt length.

[SCzEngrgGroup]

I think the calculation are right, since he did not calc belt length.

Actually, no. Based on the stated pulley diameters, even his RPM calculations are off a bit, assuming a 1750RPM motor.

Regards,
Ray L.

[pete from TN]

Well there are several ways to accomplish this. The Tormach machine for instance has a swing away power drawbar cylinder that makes it possible to manually access the drawbar top to use for instance r8 tooling if you choose to. Just because you intend to use a power drawbar and the scissor clamping setup does not mean it needs to be permanently attached to the spindle body at all. It can be in fact floating on the top of the spindle body as mine will be if I ever get it finished. The choice is yours as to how you intend to do it of course but it does not HAVE to be permanently attached. Right now having the ability to easily remove and inspect the spindle bearings as well as other features is very nice. Understand tho that the coupler I used is not large enough to fit on the IH sized machines apparently. You would have to verify fit on the MTW machine. There is always more than one way to accomplish something...peace

Pete

[skray775]

Sorry that was a cut and past from the original belt calculation and I forgot to remove the belt lengths. You are correct the belt length will be the same.

My belt pulley and belt calculations came from here:
Pulley And Belt Information Calculator

You're doing something wrong in your calculations. If you're swapping pulleys between the motor and spindle, the belt length will be identical in either configuration.

Regards,
Ray L.

[skray775]

I think I found your thread and was reading it last night. Very nice! I think I will use your ratio. So much good info in all the threads but it is hard to find because they are so large!

I went with 1:2 & 2:1 ratios .. That way you have the exact same belt length so very little motor movement is required to switch.
I also used a 2hp 3ph 1725 rpm motor like you, and I changed out the bearings in the spindle to MUCH higher quality A/C bearings.

At 2:1 (motor to spindle) ratio I get down to 280 rpm with pretty good torque & at the 1:2 ratio I get up to 8000 rpm.
I believe that's running the VFD from 20hz to 130hz if I remember correctly.
If you think about it the motor is only turning at 4000 rpm to produce 8000 at the spindle that way. Standard motor bearings are good to 5500 rpm.
I've been told by motor repair guys that in these general use low hp motors they all have the same bearings regardless of whether their rated at 1725 or 3450.

I just ran a part today using 1/8" ball endmill & the machine cruised along at 8000 rpm for several hours.
Spindle, Motor, & VFD were hardly warm to the touch when done.

[jid2]

Is everyone using inverter motors, or are some using standard motors? I know Jermie used an Inverter, with that Marathon Black Max he scored. What models of Baldors specifically are you guys running?

[gd.marsh]

jid2,

This would be an example in the Leeson brand name .. you want to stay away from the heavy frames unless you happen upon one cast in aluminum.

LEESON 110451, 2HP 1725RPM 56C TEFC 3PH MOTOR - Electric Motor Wholesale

Shop e-bay & you'll probably beat this price.

[skray775]

Over the last few days I have been drawing and choosing parts for the conversion.

Ball Screws for the X and Y will be 20mm and 25mm for the Z.
I think I am going with 15x35x11 Nachi angular contact bearings for the 20mm screws. Not sure about the Z bearings.

While poking around the barn I saw an old 3 phase radial arm saw that is basically scrap but started looking at the table, 48" x 30" and 30" high. It is pretty heavy duty and I think it will work nicely.

[Maglin]

That is a nice score on the table. Looking forward to seeing how it all plays out.

[skray775]

Fabco air cylinder purchased for $100 on eBay.

MP4x2x4x1FF-MR-PA2

[dwalsh62]

Wow, you sure do get busy with multiple projects.

Inspired by your mill modifications and various projects I set out to make a CNC mill from scratch.

I cast pieces in steel when I can, machine everything else, I use GSK-980MD panels (because I can get them for $1400.00 shipped), 1KW 90mm AC servo motors (I can get 3 sets of motors and drivers for $1900.00 shipped).

This is a scratch build and this is what I have 3 days into the project including casting of parts.

A solid milled table (420mm x 220mm with 420mm x 220mm travel), THK 20MM linear rails (I have a solid over-seas source for any THK linear rails at a reasonable price), RM1605 ballscrews for X/Y, RM2005 for Z, custom ballscrew coupler with integrated end nut and locking set-screw, BK/BF bearing blocks, cast steel spindle head, cast steel base and cast steel column.

The spindle is a 220V, 4HP, ER20, 350RPM-9,000RPM spindle made to my specifications (I have an in with the manufacturer).

A small home-made powder-coating oven, four quartz elements from two toaster ovens and one of the controls, it makes things look pretty and the gun is nothing more than a cheapy ($74.99) from harbor freight.

Cutting fluid seems to make things rust almost immediately so anything that isn't painted needs an acid bath and quick dip in copper sulfide to keep it looking good and this will be done before the final assembly to the table and any other non-painted part that requires it.

Your comments, suggestions and opinions are welcomed and encouraged.

-- Dale

[skray775]

As I continue to work on the drawing I have found 2 things that are a bit annoying and may sway people's decision to go with these mills based on the advertised 30" x 12" work envelope.

First lets talk about the X axis at 30". The table it 39.5" wide, the cross slide for the Y axis is 14.5" wide, If you subtract the cross slide from the table you get a work envelope of 25" not 30". You have to over drive the table 2.5" past each end if the cross slide in order to get the 30" advertised travel. That is kinda BS with a table this long and heavy. The same holds true for the Y axis to a lesser degree.

Now on to the Z axis. The Z is advertised as 22" tall but with the head all the way down the spindle is about 3.75" above the table. The column has a cross member cast in place (see picture) that could be removed.

The problem with removing the cross brace is that the dovetails on the column do not go down any further so even if you get the head to come down lower by removing the brace it will be hanging off the lower end of the dove tails.

So a little math, top of table to spindle = 3.75" minus my shortest TTS tool holder. My shortest TTS holder and mill combo is about 2.5".
3.75 - 2.5 = 1.25" That would mean all work would have to be raised a minimum of 1.25" off the face of the table.

For the Z axis I could :
1) Live with it and make some 1.5" thick tool plates for the table.
2) Extend the quill 1.5" installing a spacer between the head and quill then lock the quill it in place - I would loose space up top for the pulleys.
3) Cut out the cross member and let the head hang below the dove tails - eww :bs:

[arizonavideo]

You could do what I did for the Z and make a L shaped Z ball screw mount and add a second bolt about 1" higher up.

This lets the slide go lower by the amount of the offset in the L shaped ball mount and you get extra strength from having two bolts.

I just didn't like the single bolt idea for the stock mount.

So now I can run my Z slide off the dove tails by abut a inch.

IH cuts out the cross support which will over travel to the table if you wish.