Announcement

Collapse
No announcement yet.

My twist on the cheap power drawbar

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • torker
    replied
    Thanks Marc!

    Leave a comment:


  • Marc M
    replied
    Originally posted by Wirecutter


    Everybody has been raving about the cheap power drawbar project. I've been going crazy here and I still can't get it to work. The butterfly wrench works fine on it's own, and it can operate the drawbar on my Bridgeport reliably without even having to engage the spindle brake. But when the valve body gets "remoted" to the other end of some tube, I can't move enough air to operate the wrench properly. I've checked hole alignment everwhere, and even remade parts.

    I guess nobody else has seen this problem, right? There must be a reason that everyone deviates from the original plans in some way or another. Are people cheating by running higher than recommended air pressure?

    -Mark
    Mark,

    When I redrew the prints to match my impact, I forgot to draw in a couple of holes. After getting it all together I had a similar problem. The wrench was weak and the cylinder could barely push the thing down, sometimes not at all. At first I thought it might have been due to the smaller bore cylinder I used, but after some experimentation I discovered the missing holes. Double check your parts to be sure they match the prints. If you don't have the vents, that will cause the problem. My compressor kicks in at 90, out around 120. Not sure if that qualifies as cheating.

    The reasons I changed the plans had nothing to do with performance. First I used a different air cylinder than what was spec'd because it was cheap ($10 for 2). The mounting was different so I wanted to incorporate that. It was also dual acting so it lacked an internal return spring necessitating the use of external springs. Second, I didn't like the idea of having to solder the small copper lines because they're not easily removed. Also, I didn't have any copper, but had plenty of 1/8" plastic, inserts and fittings. Besides, I've just never been one to read instructions, let alone follow them

    Torker, the original design is based on a cylinder with a little over a 1" bore and a 1" stroke. The pair I picked up had a 3/4" bore, 2" stroke. The extra overall length created problems so stick with the 1" and you should be fine.

    Marc -

    Leave a comment:


  • Bill Pace
    replied
    I'm in the final stages on one also ---this thread kinda booted me in the butt to do one.

    I had a bit of head scratching getting it to fit on the mill head...I've got the new ENCO 9x42 and it has the back gear lever/apparatus on top with a ---er..bearing tower?? that had a plastic cover over it all, held on with three 8mm screws (which I have removed), requiring a 3-legged mount in those holes, which needed,-- at least a little bit-- of adjustment capability. Finally got that going OK and now waiting on the BBT (big brown truck) for the air cyl, before I can make any finalized fit-ups.

    Mark, let us/me know about the air --or lack of -- problem in case I run into it.

    Leave a comment:


  • torker
    replied
    Mark...this should be interesting. I don't have any plans and was just sitting here drawing up some ideas....on a napkin...lol! I have no idea really but I'm wondering if you have an air leak internally that is channeling air to the wrench in both directions? Or maybe the cylinder is getting the most air or... well this should be interesting!
    BTW...the cylynders you guys use. Do they have a 1" stroke? How long are they (roughly)?
    Thanks!
    Russ

    Leave a comment:


  • Wirecutter
    replied
    Feeling like an idiot...again



    Everybody has been raving about the cheap power drawbar project. I've been going crazy here and I still can't get it to work. The butterfly wrench works fine on it's own, and it can operate the drawbar on my Bridgeport reliably without even having to engage the spindle brake. But when the valve body gets "remoted" to the other end of some tube, I can't move enough air to operate the wrench properly. I've checked hole alignment everwhere, and even remade parts.

    I guess nobody else has seen this problem, right? There must be a reason that everyone deviates from the original plans in some way or another. Are people cheating by running higher than recommended air pressure?

    -Mark

    Leave a comment:


  • Marc M
    replied
    Good eye Brian. I didn't have a 3/4" 12pt 3/8 drive deep well socket so I tried the 6 pt. My brother brought a 12pt from work to try. It was better, but didn't eliminate the problem. I bought a 12pt off Fleabay. It's supposed to be a nice toasty 21 deg f here tomorrow (-5 right now) so I'll head out to the shop and try a few things to see if I can improve the performance.

    Iowolf, after looking to see what the top of the Wells looked like, you're right, you have your work cut out for you. Shouldn't be too bad if you don't mind putting a few extra holes in your machine. Otherwise, better you than me!

    Marc -

    Leave a comment:


  • Guest's Avatar
    Guest replied
    The hard part is adapting it to a Wells Index 747 V/S or 847 V/S.

    Leave a comment:


  • carlquib
    replied
    Hi Marc,

    I was just looking at the pictures that of your power draw bar and it looks like you are using a six point socket instead of a twelve point could just be the lighting for the pic. Do you suppose that might be why your socket doesn't smoothly engage all the time? I was just curious because I am working on one of these power draw bars and like the looks of your refinements.

    -brian

    Leave a comment:


  • Marc M
    replied
    I initially was going to just scambo the idea and not use the plans. I just didn't feel right about it. I would never have come up with such a simple approach having a propensity to over-complicate things so it's only fair.

    Bob, I thought about pressing some bushings in the plate, but tried to stick with the KISS principle. With the additional bearing surface the thicker plate provides, it slides very smoothly. I also thought about wear, but it's not in a production environment and it's certainly not a precision mechanism anyway.

    As far as centering the drawbar, the way the drawbar is setup on my BP clone, it doesn't have much radial play. I'm leaning towards the cylinder being a bit light. When I get back to the shop I'll try to verify it. Assuming that's the problem, if the addition of the check valves still don't provide enough, I'll simply add the other cylinder. I had that in mind with my design so it will be easy to add the second.

    Thanks for the input everyone,

    Marc -

    Leave a comment:


  • BobWarfield
    replied
    Here is mine:



    Works fantastically well. A couple of notes I had on it are on the web page:

    http://www.thewarfields.com/cnccookb...llDrawbar.html

    I found it an easy project and had no problems with the plans. I agree it could easily be made with bandsaw and drill or drill press. The only issue on mine was I wound up installing auxilliary springs as I see here to get the return to work well. That was no biggie. Marc, I would think that thicker block potentially with some pressed in bronze bushings or maybe some kind of delrin-type plastic could be made to run very smoothly.

    One hint I got on this board that really helps out the powered drawbar is to turn a little bushing for the drawbar to keep it centered:



    Mine would hang up slightly every now and again and eventually right itself, but I worried it was chewing up the soft drawbar nut. The bushing makes it all tremendously smooter. It took all of half an hour with the lathe to crank it out.

    Love these drawbars!

    Now if only my mill had a power Z-axis to raise the head. Hmmm. Oh well, I'm planning on CNC so it isn't worth the trouble.

    Best,

    BW

    Leave a comment:


  • torker
    replied
    Geez...I'm jealous! I keep promising myself that I'll buy a BP clone and build one of those to fit. The BP clone hasn't materialized yet but my frustration level is mounting.
    I'm almost ready to figure out how to mount one of those to my mill/drill.
    Yeesh, last night I worked for hours on that boring head and did about 4 million cutter and 2 million holder changes...seemed like that many...
    I started thinking about you guys and your power drawbars. Those are so slick! My hat is off to you guys for "rollin yer own"! Good work guys...you are a credit to this board.
    Russ

    Leave a comment:


  • Wirecutter
    replied
    Marc -
    I'm also building up the power drawbar and have had my little trials and tribulations.

    1. It took a couple of tries to get enough of the right fittings for the 3/8" to plastic tube right angle fittings.
    2. I found missing and wrong dimensions. If I'd written the plans, I wouldn't have put dimensions down for the holes that really have to be transferred from the wrench.
    3. I started to try to make the plates all precise-like using the mill, calipers, and the like. This project is really one for the band saw, the cordless drill, and a belt sander.
    4. I actually got the 1/8" copper tubing (which McMaster sells in min lengths of 50'). I like the idea of the thicker plate and plastic tubing a lot better - no need to solder for assembly or desolder for disassembly.

    I don't know - I guess I was expecting better for what I paid for the plans. I would rather have paid less for a more general plan - the basic idea of using backpressure from the wrench to drive the cylinder is a good one. If you decide to switch over, a good air cylinder to use is McMaster 6498K171 - I believe that's the one I got.

    I found the same problem with Horror Fright - it took forever to ship the $30 wrench. I guess I'm spoiled getting all those shipments from MSC and McMaster overnight.

    I'm a little slow lately, but I'll try to post photos when I get my power drawbar done.

    -Mark

    Leave a comment:


  • Marc M
    started a topic My twist on the cheap power drawbar

    My twist on the cheap power drawbar

    The cheap power drawbar that Joe Vicar came up with (http://home.insightbb.com/~joevicar3/cheap_drawbar.htm) has been on my 'to do' list of projects that sits nicely on the back burner. After making a part for my brother that required a lot of tool changes, the drawbar project became a priority. I ordered the impact from HF, the plans from Joe, and searched Fleabay for a cylinder. I found a pair of Bimba .75 x 2" dual acting cylinders for $10 shipped. A bit different from what Joe called for in his plans, but I felt it would work fine and the price was right.

    It took 2 weeks for HF to get the impact shipped. In the meantime, I got some of the stock chopped up and sized for the project. Since I had the prints from Joe, I was going to go ahead and do all the drilling, tapping and countersinks on the various plates but in the end decided I should wait. It turned out to be a prudent decision because the screw locations on the impact did not match the prints. It appears there is some variation in these cheap impacts so be sure to measure yours and modify the prints as required. I ended up redrawing everything in AutoCad with the new dimensions and the different cylinder mounting to avoid any confusion or mistakes.

    I also changed the design of the feed to the cylinder for several reasons. First, I have plenty of 1/8" plastic tubing laying around but no copper. Second, using plastic allows it to be easily taken apart if necassary. Finally, I wanted to incorporate check balls to isolate one side from the other for more efficient operation. To facilitate this, I used a thicker mounting plate for the impact. This allowed a second set of fittings to feed the cylinder to be installed in the side of the plate. It also provided plenty of room to install a check ball & spring. Here's the final product:





    Because I used a different cylinder, I had to add return springs. The other problem I ran into was it's length. Because it's much longer than what's called for, it hit the mounting plate before the socket could engage. I could have changed the base plate to allow clearance for it, but took the easy path and just used a deep well socket. I was concerned about it flying off due to the extra length but it hasn't been an issue. There is still a chance that the socket will crack at some point so I may have to change it later. In the preliminary testing, it seems to work fine.



    I mounted the operating valve right by the spindle brake so they could both be operated by the same hand. With my limited testing, so far it's not been necassary to tap the drawbar to release tooling. The downward pressure and the action of the impact seem to be enough to dislodge things. I have had some problems with the socket not engaging the drawbar when removing tooling, just skipping across the top. It might be due to the fact I'm using a smaller cylinder than what was called for. I haven't found light enough springs for my ball check valves yet either so they haven't been installed. I'm hoping that once they're installed, they'll increase the efficiency of the apply circuit enough to make up for the smaller bore.

    This is a great project and extremely useful. I wish I would have made it back when I first ran across it. I definitely recommend using the correct cylinder for the best operation. If you have some thicker plate, I think the plastic airline approach is a better solution.

    Have Fun!

    Marc -
Working...
X