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Harbor Freight 44991 Backlash

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Getsome

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#1
OK, i'm brand new to machining. I purchased this mill as a learner. I'v been dealing with different issues that i'm assuming all beginners experience. I upgraded to the belt conversion kit right away. Now that I've actually been using this mill, i'm dealing with some backlash issues, and the head walking downward while I'm milling. So I just bought the spring conversion kit, or should I say I just ordered it. Now I'm looking at the upgraded anti backlash nuts. The question I have is, should I continue to put money into this cheap mill or buy a better quality mill and convert this one to CNC? I will have as much in this cheap thing as I would to just buy a better quality. What say you?
 

Bill W.

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#2
First of all... welcome to the forum. As you are well aware of, HF machinery, out of the box leaves something to be desired. If the machine you have is capable of doing everything you desire, then bringing it into the required tolerances will cost some time and money. If looking ahead and you can clearly see something a little bigger and better, it might be wise to limit the amount invested (time and money) and put it toward something better. In the mean time get it to the point where it does what you want it to do for now and save for the future. Just remember, when you go to sell it, there is a limit what you will get in return on your investment. Enjoy it for now, learn all you can and look to the future... Good luck and enjoy!!! Bill W.
 

JimDawson

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#3
That one is a tough call. It really depends on your budget, your needs, and your space. If it's in the budget, then a Bridgeport or clone would be better. CNCing your machine would be a fun project.

As far as the backlash issues, some backlash is normal. 0.010 to 0.050 would be in the range of what I would expect for a good machine. I have run machines with much more backlash than that and you just have to approach the work in a direction to compensate for the backlash. Also, are you trying to climb cut with your machine? That won't work except for very light cuts. The cutter should should be rotating against the direction of feed rather than the cutter trying to pull the feed along.

The head walking down is not normal assuming you have the lock set. If the lock is not set, then try that. The cutting forces tend to pull the end mill into the work, but the lock should overcome that force.
 

RJSakowski

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#4
Regarding the pulling down of the milling cutter while milling, you should be aware that cutting forces can also pull the cutter in the chuck when side milling. Drill chucks are not ideal for holding end mills. A set of R8 end mill holders in convenient sizes is a good addition to your tooling. End mills with small flats on the shank (Weldon type), combined with a setscrew type end mill holder will resist pullout forces.
 

royesses

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#5
Are you locking the head with the lock bolt? Are you using the drill chuck to hold the end mills? The lock bolt presses against the gibs and should stop the head from moving. Set the depth, lock the gib, make the cut. I think I understand that is what you are saying. The backlash is adjustable to an extent with the double lock nuts on the x and y hand wheels. They work much better when using a ny-lock instead of the two nuts. There are also adjustments for the x and y axis screw nuts and a lock screw for each, if the lock screws are loose they will have a lot of backlash. If you install a set of dro's the backlash no longer matters. The Igaging dro's are an inexpensive but nice upgrade. Get a set of R-8 coletts to hold your end mills. Little machine shop has them at reasonable prices:
http://www.littlemachineshop.com/products/product_view.php?ProductID=1604&category=

Welcome to the forum! Lots of help and great guys and gals here.
 

Baithog

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#6
The head should not 'walk down' under load if you have tightened the z-axis lock lever. Having the fine feed engaged mostly stops any drop in the head and tightening the lock absolutely prevents it. As above, the cutting forces can pull a cutter right out of the R-8 chuck, especially an import collet like most of us start with. An endmill holder and Weldon type mills prevent that . One of my better investments was a 3/8 and a 1/2 inch holder. The spring kit is nice, but it will not fix the pull-out problem.

You do not have anti-backlash nuts on the unmodified version of the mill. The nuts can be slit and turned into a mostly useful adjustable nut, but that is not where the problem is in most reasonably well maintained mills of that type. Much of the backlash is usually in the thrust bearing preload. The nuts that hold the hand wheels on also set the preload. Getting the load set and the locking nut tight is tricky. The remaining backlash is in the nuts and you can probably live with it. I never had more than 0.010 of backlash, which is easy to compensate for in a manual machine. Not so with CNC, which likes minimal backlash for accuracy.

The move to CNC for the mill should not be undertaken until you have made some small projects to plan. It is not a cure all for a sloppy mill. I converted mine. I did it in 2 stages. The first stage used the screws, nuts, and factory dovetails. It worked and I was able to produce a pistol receiver to plan from it. The stock screws had barely tolerable backlash, the acme screws sucked op torque, and the dovetails sucked. Stage 2 lengthened the Y-axis, re-cut and scraped the dovetails, installed ball screws, added rotation to the head, and converted to belt drive. Before you head off down the CNC road, there are some considerations. The mechanical parts in kit form cost as much as the mill did new. Import and home brew versions of the mechanicals are about half that. You trade shop time and aggravation for cost. The electronics to drive the machine will be in the neighborhood of twice the cost of the mill. Again, you can save money with low end import boards, but may have to buy replacement boards in short order. The software to run the machine will be at least the cost of the mill. All told, I would recommend that you set aside $2K for the project. That's a lot of money, but not as much as the $4K factory CNC from LMS. On top of that, if you make your own mechanicals instead of a bolt on kit, You will need a lathe and a second mill, preferable a larger one. I did mine with a G759 (G704 w/dro) It would have been easier if I had access to a knee mill.
 
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Mariah

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#7
Getsome, When you are ready to go CNC you may want to check Syil. Just 2 years ago I got a Syil X6 VMC and it has turned out to be a real work horse. It is sturdy and accurate for the work I do and that's cutting clutch splines in drill rod. They make smaller bench models for entry level needs that might be the best suited for you if cost vs time and effort appeal to you.

Mariah
 

Getsome

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#8
Thanks for all of the good advice from everyone. Here is a little more on my situation. I am using an R8 collet set I purchased from Little Machine shop. My intentions from the beginning were to CNC this mill. I already have the Fusion Kit, and I purchased a stepper motor kit with all he hardware from one of the suppliers on Amazon, and yes, it was much more than the cost of the mill. I had a heart attack that put that project on hold. I'm just getting back around to using/playing with this mill.

I have always wanted to learn machine work as a hobby. Since there are no vocational schools in my area that offer these type classes, I decided to teach myself. I hope to retire in the next 10 years so I have started to purchase some machines to learn on, hoping to upgrade once I retire. I also have a Grizzly G0752 lathe. I've been reading some books and watching youtube, teaching myself. That's what brought me to this forum, the thirst for knowledge. Once I started practicing and playing with the 2 machines I have, I am hooked. I own my own company so my budget is pretty liberal. If I were to purchase a new machine before the end of the year, it would help with the taxes i'm paying. I am not looking to go Bridge Port, I am looking for a bench top mill with power feed tables of decent quality. Is there something in the $3-4K range that anyone would recommend?

On another note, I have realized that locking the head nut in place has stopped the mill head from moving downward. Being a beginner, I didn't realize that I would have to do that on every pass. The table backlash is not that bad, just enough to be aggravating. I guess I expected it to be more like my lathe, were the hand dial gauges are very close.
 
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