Can someone talk to me about “power draw bars”?

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3Dogs

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I’m in the planning stages of getting a new bench mill and converting it to CNC (probably a PM-833TV).
I have a product I want to machine that will take maybe 5 different tools (roughing mill, finish mill, thread mill, drill bit, very small mill). I’d (naturally) like to minimize tool change time. I see videos of people with a power draw bar on this mill popping tools in and out quickly. What I don’t understand is: what systems work with the power draw bar kits (Priest) for this mill. Does it come with a new chuck? I hear talk of TTS-compatible tool holders. Are these the way to go?
Is there an advantage of one system over another if I eventually want to go to full ATC?
What about ER collets? Can they be changed fast? How about presetting tools to the correct stick-out so the depth doesn’t need to be measured each time a tool is changed.
 
The PM-833TV is an R8 spindle machine. R8 collets include a 3/4" collet. The TTS type tool holders are 3/4" straight shank and commonly available with ER16 collet chuck for under $30. ER16 collets are commonly available up to 3/8" (10mm) capacity.

If each of the 5 different tools are 3/8" or 10mm max straight shank, I can't think of a much quicker/less expensive way to go with a power drawbar. Put the 3/4" collet in the spindle and swap TTS type tool holders.

I can't advise regarding an ATC upgrade.
 
You've got enough Z travel to use the TTS compatible tooling. It's a 2HP mill which is perfect. Right at the limit of what TTS tooling is good for on power and rigidity.

The sales page for the Priest on the Precision Matthews site mentions using TTS with their unit, so I'd assume that's what they are intending. Their power drawbar is VERY similar to the Tormach power drawbar design.

If you look at the TTS compatible tool holders for sale out there, you'll see some of the tool holders have a ring cut into them and some don't... that ring is for the forks on an ATC carousel to hold the tool. So you'd want holders with that ring if you intend to use an ATC with those tool holders later.

BUT Frankly, I'd just forget about ATC on that thing and focus on getting power drawbar and TTS tooling. That will make it really really easy to use. Your CNC conversion will be enough "work."

IMHO Hacking up an ATC system for it will just make it a pile of frustration and never ending project.

If you truly need reliable ATC better to buy a CNC machine built for and with ATC.

I'm also going to just say this here: If you want to make your product any time soon, don't convert a mill. BUY A CNC MILL.

If you have no concrete timeframe, and are more interested in taking a long hobby path to eventually making some of your parts and aren't concerned about when you start production or how many you make, then enjoy the journey save some money and have fun with the conversion. But you are not going to have a good business result making parts by spending all the time and resources converting a benchtop mill to CNC. There are too many things out there you can buy for only a little more money that will start making parts immediately.
 
There are also many, many job shops that can build your parts for WAY less than you’ll get into buying and converting a manual mill.

I agree, if the goal is to learn about building a CNC and you don’t have a definite timeline for the business you’re on the right path.

However, if your investor (could be you, or the wife) is planning on a return anytime soon you may want to rethink this plan.

Not knowing anything about your background that’s what comes to mind. However, you may have a machining or engineering background and have run the numbers, and decided this is the best way to go.

Cheers,

John
 
I understand the point you are making.
I talk about the part I want to make, and my reasoning here:
Hi, I’m 3Dogs

Making this part is more-or-less an excuse to buy a new mill. We could have the parts machined overseas if needed.
But, there would be advantages to doing them in-house. We are constantly tweeting the design to make the product easier to produce. Being able to try different ideas quickly would be helpful.
 
Thanks for linking your introduction, I used to have a racing go kart business in Phoenix and did business with a shop there that built some of our parts.

Looking at what you're making I'ml thinking a Tormach might be the way to go, used ones come on the market fairly often or financing (leasing) a new one might be advantageous business wise. They have a dealer right down the road from where I live now, might be worth a phone call to discuss what you'd need and if any used machines are available. https://www.santacruzelectronics.com/index.cfm They're hobby business folks too so might be able to provide some advice beyond just machine tools.

I haven't converted a bench mill, but my CNC Mill Drill project gave me a taste for how much tweaking you need to do to get a home-brew CNC working properly (spoiler alert, mine isn't yet). If I actually had parts I wanted to make it would drive me nuts figuring out if I was fighting my design, or something going on with the machine.

In any case it sounds like you've got a good grip on where you're going with this, looking forward to seeing what you end up with.

John
 
I hate to be a wet blanket 3Dogs but a power draw bar is basically a pneumatic wrench . You first mentioned you needed to keep noise down , IMO you should be looking for a small shop to rent .
Mark .
 
3Dogs said:
I’m in the planning stages of getting a new bench mill and converting it to CNC (probably a PM-833TV).
I have a product I want to machine that will take maybe 5 different tools (roughing mill, finish mill, thread mill, drill bit, very small mill). I’d (naturally) like to minimize tool change time. I see videos of people with a power draw bar on this mill popping tools in and out quickly. What I don’t understand is: what systems work with the power draw bar kits (Priest) for this mill. Does it come with a new chuck? I hear talk of TTS-compatible tool holders. Are these the way to go?
Is there an advantage of one system over another if I eventually want to go to full ATC?
What about ER collets? Can they be changed fast? How about presetting tools to the correct stick-out so the depth doesn’t need to be measured each time a tool is changed.
Click to expand...
Perhaps the attached will help a bit. Have a look.
 

Attachments

  • R8 Tool Holding Alternatives – Power Drawbars versus Quick Change.pdf
    1.3 MB · Views: 26
Sage advice from John above. If it's a hobby and you want parts right away, buy a used CNC mill. If you are looking at making a low-volume part with no plans for doing others, it'd be best to job it out if finances are a question. Sounds like you fit in well here: Most of us LOVE spending $10K+ for machines so we can spend 100's of hours in the shop to make a $0.50 part!

I have a Tormach 1100 Series 3 with an ATC and power draw bar. I bought it used around 4 years ago for $18,000. It was well tooled, had the ATC, power draw bar (PDB), 4th axis, etc. I don't use the heck out of it, mainly reproduce old Erector set parts for something to do and keep my brain active. I've made enough off it after 4 years to cover my initial investment, but I didn't buy the mill with that as a goal. For me, it's a hobby, not a business.

I bought a Bridgeport a year or two before the Tormach because I wanted one. The one I found locally happened to have a 2-axis circa 1981 Anilam CNC on it. I'd never worked on a CNC machine before, but after using it and seeing the potential, I had some buyer's remorse; I wanted the 3rd axis too! I looked at updating the controls to an Centroid Acorn system, machining some sort of quill control with a servo for the Z-axis, but wanted to make parts, not make the machine. So I bought the Tormach.

The power draw bar is a must with an ATC since the controller will be doing the tool changes. You've got a great handle on the process; the ATC lets you do "lights out" machining. I'll fire up a routine, walk away to do other stuff, and return to the mill afterwards to load in the next part.

Regarding changing tools in tool holders, I don't (very often). I have over 50 TTS tool holders and for the most part, when something goes in, it gets a tool number, gets the length checked, and becomes a permanent part of my tool table (also enter the diameter of the tool). The CNC will need to know where the tip of the tool is relative to some surface (spindle adjacent to the R8 collet on my Tormach). If I change tools in a given tool holder (dull/broken end mill, dull drill bit, etc.), I stick the new tool in, remeasure the tool length and update the tool table.

If I had limited tools and needed 5 tools for a job, I'd set each one up and enter the diameter/length into the tool table before running the job. If I had to change tools mid-run, it'd really slow things down.

Looking forward to seeing your projects!

Bruce
 
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