Hi Everyone,
I’m happy to see activity here and look forward to seeing a working tool changer soon.
I’ve been busy as a full time college student that works a full time job as well.
I only get a few hours a week to work on projects. I used my mini gantry mill Saturday to make some caster coasters for my PCNC1100. I hope to get it online in April during the spring break.
Remember: pictures, pictures, pictures
MikeAber
Great thread, and Mike, excellent info on your part. Before I order that R8 spindle box, in its stock configuration, what rpm is it safe to operate at? 6000 rpm? I would like to use a similar setup, with a KBIC, probably the 240, as they are easiest to find on ebay, and the 1.25 or 1.5 HP treadmill motor. unfortunetly, the 1.25 is not in stock, and the 1.5 link no longer works.
Get the 2.5 HP motor for $19.99 and run it at 95VDC with lower current. It's the best one anyway. I just checked, they have over 2,000 of them.Originally Posted by Enraged
http://www.surpluscenter.com/item.as...tname=electric
I've run my spindle for several hours at 6,000 rpm. You need to break-in the bearings before long runs at high speed, several hours at 3k, 4k, and 5k rpm. If you don't break-in the bearings they'll overheat and be ruined and if you don't make the top bearing a slip-fit on the spindle the bearings won't survive as there isn't any room for thermal expansion at high speed. A fan to cool the motor and spindle is also a necessity. The original bearings aren't expensive; I purchased several sets for $40.00.
Good luck,
Mike
for the bearings, if one were to replace the depp groove ball bearing with something like this: http://www.vxb.com/page/bearings/PROD/30mm/Kit7098 , do you think the modifications would still be needed? or possibly: http://www.vxb.com/page/bearings/PROD/30mm/Kit1089
also, what size of belleville washers did you use? I see that JFettig used some 495 lb springs, but I dont plan on using any sort of quickchange tools or power drawbar just yet, I need to get the machine built first
for those that are trying to make a power drawbar setup using air cylinders, have you considered a small geared motor? ive played with a few at school that, if properly geared, would provide adequate force so a big lever arm isnt needed.
This post has my bearing info:http://www.cnczone.com/forums/showpo...7&postcount=79
I ordered the washers from McMaster-Carr and the Schnorr Part # is K6204. That # relates to the size of the bearing The top bearing has a 30mm id and 62mm od. I believe these are 600# springs at max deflection and I used two of them in a back to back configuration and preloaded the spring washers lightly to maintain tension for thermal cycling.
I'm still running the original set of bearings.
Mike
Last edited by MikeAber; 03-19-2006 at 02:09 AM.
Need a new ratio for spindle.
Hi All
This thread has been a great benefit to me. I hope I can jump on this thread and ask a few questions. Just upgraded my spindle to one from the littlemachineshop. The timing pulleys I selected are setup more for my woodworking. The maximum speed of the spindle is 5000 rpms. For my test in steel I set the depth for .1 at a very slow feed of 4 ipm and cutter speed was 700 rpms. The cutter was cutting its full width at .5. I was happy with the results except for the fact that when I was almost done to my surprise the spindle slowed to a stop. It`s my guess that the grearup drive is loosing a great amount of torque due to the ratio change. So it seems I`ll have to purchase more pulleys for a gear down drive. Does someone have a recommendation for a ratio that I should use for my attempts at machining metal. I`m considering maybe a 4 inch on the spindle and a 2 to 2.5 diameter on the motor. To save cost I was thinking about using standard V belts in a small width series. The motor has a maxium speed of 2500.
Regards Barry
if you want to use 700 rpm for steel, and your motor makes the highest power at its max speed, 4:1 spindle:motor ratio would work, or a 3.75:1 would give you about 714 rpm at the spindle. www.sdp-si.com/ has a good selection of pulleys, although if you have access to a lathe you may be better off making a set.
Wow!
Usually, you won't cut a full width with a .5" end mill and a .5" end mill is a large cutting tool for steel in a DIY gantry machine. You didn't say how many flutes the end mill had, if it was High Speed Steel or Carbide, and the alloy of steel you were using for your test. If it had 4 flutes you are in the ball park on the speed and feed. If it had 2 flutes it may have been too fast on the feed. Normal feed of the cutter (stepover) would be 66 - 75% of the cutter diameter. If you need to feed the cutting tool full width take lighter cuts. A good indication of how the mill is doing is the color of the chips. With HSS a yellow or "straw" color indicates you are at the limit of the cutting tool's capability.
I'm certainly no expert; however, I'll guess your chips were "straw" color or brown and the hardness of the cutting edges were "drawn down" by the high heat resulting in a breakdown of the cutting edges. Straw color with HSS = slow down or reduce depth of cut. Blue chips with carbide mean the same. This is a general rule for mild steel.
It looks like you have plenty of horsepower. How about a two speed belt drive with 2" and 4" sheaves on the spindle and on the motor with one side flipped over for 2:1 and 1:2 ratios with a belt change.
Attached is a general speed/feed document if you are interested. This is real basic information. The machinery's handbook is the bible.
Mike
Last edited by MikeAber; 03-19-2006 at 02:30 AM.
Agreed Mike. 0.1" deep, 0.5" wide on any steel is very good for a homemade machine. Barry, how did you cool it? or did you go dry too?
JR
Hi JR,
Good point! I assumed the cutter was running dry as coolant on a gantry machine is not the norm but you're right. The formulas assume coolant is being used.
What's new JR? Doing anything exciting? I have projects lined up beyond my years.
You meet the nicest people in the ZONE!
Mike
Pulleys
Hi
The cutter was a four flute endmill with no coolant. I`ve done some lathe work on my old south bend but never got
my hands on a milling machine. Milling is unchartered ground ...so this is all new to me.
That`s great info on cutter speeds ....thanks mike. I just started doing research on new pulleys.
I took mikes recommendation and hit the internet for info. Due to a height requirement with the spindle
nut it looks like I have approximately one 1 inch to work with.
Most of the step pulleys are 3 or 4 steps and it seems they don`t graduate in large enough jumps
to match our specs 2 to 2.5 to 4. I was thinking about turning a pair but have no aluminum for the attempt.
Its looking like I`ll have to purchase a single groove sheave for each and just change all the pulleys
when necessary. I just saw a thread in another usergroup that the small series v belts are quieter then
timing belts so that`s a benefit. I know the size of the v belt has a direct correlation to hp. I checked my
Powermatic 3 hp shaper and the belt size was small...about 5/16 wide.
Many Options
Hi Barry,
I wouldn't change anything for now, check to see if the edges on the bottom .100" of the end mill are dull from your first experience and do more testing with a lighter cut .075" deep or .050" deep. Going to a smaller end mill - .375" or .250”- would allow you to increase rpm and feed rate as SFPM (Surface Feet Per Minute) would decrease with a smaller diameter. Without coolant the SFPM should be reduced.
The gantry mill design can't typically compete with the mass and rigidity of iron machines for brute force operations; however, the gantry design excels at speed. Look at using smaller end mills at higher rpm and higher feed rates to accomplish the same amount of work in the same amount of time with the same chip load per tooth. The advantage of doing this is much less dynamic force acting upon your machine's weakness (rigidity). Tool life is reduced but smaller end mills cost less and carbide end mills are almost the same price as HSS end mills in the smaller sizes these days.
Your machine looks great! I can see you used quality materials in its construction.
A two speed belt drive would optimize the torque of your motor for the job at hand. With your lathe you could get a cheap set of die cast zinc sheaves and turn down a 3 step sheave with a 4" largest pulley to a 2 step sheave with 4" and 2" pulleys. Look at the Little Machine Shop 2 speed conversion kit for your spindle for ideas. http://www.littlemachineshop.com/pro...ProductID=2560
I would make a set of pulleys to fit the QD bushings you already have for V-belts or purchase a set of V-belt pulleys for your QD bushings and swap pulleys when you want to make a ratio change.
Just some rambling, have fun
Mike
how many Hp Spindle motor need? to cut metal
what type of metal do you want to cut? it really depends on material, feeds and speeds, depth of cut, cutter size, etc.
The tooling that you are going to use effects it greatly as well, to use a 1/4" carbide bit spinnng at say 7000 rpm in steel, you won't need as much brute force, bucause the load per tooth will be less. There will be a limit to the power you can actually use, if you have a huge motor with flex in your machine, the motor size benifits won't be seen, because the machine will flex when you try to make deeper cuts.
Can I watch you cut steel at 7000rpm? it may be fun
Yeah me 2. While some of the newer coating tools do suggest higher speeds, that much might not do too good.
Speaking of which, consider the speed range you need when building your spindle too. Many of the high-end spindles can't do lower that 8K RPM or so. On the flip side, an 8K max RPM spindle will cut -if slow- just about anything. Keep this in mind when selecting your motor and bearings - you might not need ABEC-7, ultra high speed ones.
JR
(Hey Mike, all good thanks. Cutting wood projects mostly but no CNC machine improvements at the moment. Share some your projects to give us ideas)
We have a cutter at work that cuts at 6000 to 7000 rpm, without coolant in steel with feed rates around 60ipm. The cuts are the full cutter width in 1/4 inch thick steel. In aluminum with small carbide cutters we go as fast as the machine will go, if that is 20,000 rpm that is great. These speeds can't be used without a super ridged machine with high hp. With smaller cutters, the rpms necessary to cut fast increase significantly.
whats the cutter and the exact speed feed you use.... I use some dry cutters that are awsome but nothing that is in the 6000+ range
thanks
Michael T.
"If you don't stand for something, chances are, you'll fall for anything!"
I agree with JRogue about spindle speeds.
Everyone seems to think a DIY machine spindle needs to be at least 10,000 rpm with the capability to make heavy cuts in mild steel. There are industrial machines with this capability; however, this thread is about DIY machines and DIY machines in most cases, are about cost.
You can have high speed and low speed capability with low cost by using two spindles.
The mini mill spindle is a good choice for DIY low speed work with some brute force capability up to 3k - 4k rpm and light duty at 5k - 6k rpms without bearing changes. 1 HP variable speed routers offer DIY machines 8k - 30k rpm capability in the same physical size as the mini mill spindle.
Make interchangable mounts for the low speed and high speed spindles for your Z axis; then there are no excuses why you can't make chips out of any material.
Mike
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