Mill Drill Questions

[Novah]

Hi - I am new to the CNC forums and am here because I want to buy a mill / drill and convert it to CNC. I have been reading everything I can find on the subjects and am feeling comfortable with how I am going to proceed.

I wasn't sure what my first post would be about but that has changed because of what happened at work today. A co-worker has offered to sell me a Jet mill / drill. It is a JMP-20VS-1. It is a 1996 model and has limited use. He bought a Bridgeport and wants to sell the Jet. It is a heavy machine with table size and travels at the high end of what the typical mill/drills seem to have. However, there are a couple of things that I need advise on.

It weighs 888 pounds which I thought was good for mass to help with vibration but the column is 4 inches instead of the 4.5 inches that seems to be the norm for mill / drills in this size. Is the smaller column going to allow more flexing?

The motor is 1.5 horsepower. I was planning on buying a new machine with 2 horsepower. Is there a big difference between the two?

Finally, it has a variable speed drive and a top speed of 2000 rpm. I haven't seen a variable speed drive on a mill drill. Should I be concerned? What about the the 2000 rpm top speed, is that enough? Some machines have 2500 rpm.

Thanks for your help, Dave

[Ken_Shea]

Hi Novah,
I could not find a jet model that matches your number, do you have a link so we can see what it is your are referring to. They do make a drill with similar numbers ??

Ken

[Novah]

I just got home and looked on the web a little. I couldn't find this model either. I reviewed the owners manual with the guy so I know the model is correct.
I did find a Jet variable speed drill press. The top of the drill press has the same variable speed control and belt cover that I remember from the manual and the digital pictures he brought it. You can see it here. http://www.blueridgemachinery.com/JDP-20VS1.gif. The JMD-18 at the top of the page looks like the rest of the mill drill. But, the swing is 20 inches.

I may have uploaded pictures using the attach files feature but in the preview post mode, they are not showing so I am not sure if they are actually attached.

I will look some more but this is all I can find right now. I may be able to borrow the manual to scan some pages and attach them to a future post.

Thanks for the quick reply, Dave

[Ken_Shea]

Dave,
If that is a similar model, it is a floor model drill press and not intended for milling. There is also no way that unit weight 888 pounds. This is not what I would consider a suitable unit for milling or converting to CNC, there is just nothing about it that lends itself to milling. A nice drill press, but that is all it is.

Ken

[Novah]

I think I confused the issue with the drill press references.

1. I am looking at a real mill drill with a 20" swing. It's manual said it ways 880 pounds. It has a table that is bigger and has more travel than say a Grizzley 1006 or or a harbor freight 33686. It has a variable speed drive with a 1 1/2 horse motor. I may have mistakenly typed the model in. It is a JMD-20vs-1 and not the JMP I originally posted.

2. My biggest concern is it has a 4 inch column instead of the 4 1/2 inch column the others in this class seem to have. Even the new Jets have the 4 1/2 so I am thinking Jet realized they made a mistake with the 4 inch and upped it to 4 1/2.

3. My second biggest concern is the variable speed drive. I can't find a Jet mill drill with the variable speed drive from the suppliers I have visited. Was it a bad idea that was discontinued on the mill drill but continued to be offered on the drill press.

I found a picture of a used mill on the web. Keep in mind that the one I am looking at is white and looks brand new.

Should I be concerned or should I get this lightly used machine that looks like new?

Dave

[Ken_Shea]

Dave,
That looks much better After re-reading your post I had kinda thought I was confusing your intent.

I would not be particularly concerned about the .5" difference in column size, although a box type column is more rigid.

I would be concerned about parts availability, so a call to jet would be a good idea about this.

My experience with the mechanical type variable speeds are they are mostly trouble free. Being discontinued is usually not a design problem more often then not it is related to cost/profit.

2000rpm is a little on the low side but is usable.

It is heavier then most and that is a plus.

Every machine has limits, you just need to work within those limits and all usually goes well.

What price is he asking ?
Very similar units can be bought very reasonably and come with a warranty so if you are not saving a substantial amount I would re-think this purchase.

Ken

[Novah]

He wants $500 for it. Up till now, my choice is the following machine. http://wttool.com/p/3006-0005. I picked this machine because it seemed to be as rugged as most with a good sized opertional envelop. Plus, Wholesale Tool is 70 miles from my house so I can pick it up and the $899 seemed ballpark. What has swayed me on the Jet is:

1. Extra mass at 170 pounds heavier. I see a lot of vibration comments when people are trashing mill drills.
2. Extra 1.5 inches in "Y" and maybe 3 more in "X" , both of which I thought was good to make up lost travel when I add ball screws with doubled up ball nuts for the CNC conversion. I figured this would help keep me from outgrowing the machine.
3. Extra 2 inches from spindle to table to accomadate vice or rotary table. Again, seemed good to prevent the envelop from shrinking too much with accessories.
4. It has seem very limited use as the individual is "on the road" a lot. He brought a sheet of digital pictures in and the machine looks brand new. I have known this individual a long time and we both share the same values so I am confident it is a good as it looks.
5. It comes with a set of collets and a face mill.

How much do you think the 2000 rpm limit will compromise my machining?
Will the lower horsepower be noticeable?

Thanks for your help, Dave

[Ken_Shea]

Dave,
The 2000rpm limit may not be an issue at all, it depends on what you are cutting, cutting tools and how aggressive you want to cut, there are other limiting consideration with lower RPM's for sure but generally speaking, the RPM has more of an effect on the feed speed then quality of cut. My mill is 4000 rpm limit, I have to work within this as well, so do those with 6000 and up, like I said they all have limits so I would not let this be a put off for you. You can always increase it later when/if you decide to purchase it.


Ken

[Novah]

Ken - In your opinion, which machine would be better? Am I placing too much emphasis on the extra weight and envelop size? My initial plans are to make aluminum molds but there will be some machining in mild steel for other jobs.

Thanks for continuing to reply to all my questions. Dave

[Ken_Shea]

I would lean toward the Jet at this point, the additional 500rpm is not that big a deal. The Jet is saving a substantial amount, some accs, local and you know who you are purchasing it from.

I have no experience in mold making but the ones I have seen are almost mirror like in finish quality, I have doubts this will be possible with 2000rpm, 2500rpm or my 4000rpm for that matter, so hand finishing will likely be required, I know there are those with experienced on this forum, so hopefully they will see your post and reply. I would be interested as well in their opinion.

Ken

[Novah]

Thanks for all your input Ken. I think the Jet will be the one, especially since he is delivering it and that means I will have helper to get it on to a bench or a stand or ?????? That is my next decision - what to put it on. Dave