Harbor freight 44991 Mini mill is a 2-speed benchtop drill/mill designed by Central Machinery USA.
With very affordable pricing and easy assembly, this machine is very popular among metalworking hobbyists.
In this article I talk in-depth about Harbor Freight 44991, I also talk about converting the machine into a CNC mill.
MellowPine is reader-supported. When you buy through links on my site, I may earn an affiliate commission at no extra cost to you.
Harbor Freight 44991 Two Speed Mini Mill Review
I reviewed this machine on various parameters like size, build quality, axes motion, dust collection mechanism, the community around it, and many more.
Size of the Machine
With a footprint of 8 ½“ x 12” and a height of about 30 inches (when fully raised), this mini milling machine is quite compact.
The benchtop mill comes with a workbed size of 15-7/8 inches in length and 3-11/16 inches in width. This is quite good considering it is a benchtop mill.
Additionally, Harbor freight provides a lot of compatible accessories for different needs that you can use with your machine.
Overall, it is a very compact machine that you can install on a table in your garage or basement.
Harbor Freight X2 mini-mill is primarily constructed with cast iron. This provides good stability while using it on high tensile strength materials.
Due to the use of cast iron the machine weighs around 138 lbs which results in a small but rigid machine.
The reduced vibration due to the weight increases the precision of the machine as this is a hand-operated machine.
The head of the machine is not fixed. It can tilt at an angle ranging between +450 to -450. A torsion spring is used for supporting the head.
You can use this feature if you want to cut or mill at an angle. This is also useful if you want to work on an angled surface.
For changing the angle of the head, a nut is provided on the backside. The tools required for this come with the machine.
The mini mill provides an adjustable acrylic guard which can protect you from flying debris and also let you see what you are working on safely.
Alternatively, you can also custom-build your guard with a material of your choice.
Harbor freight provides T-slots of size 12 mm (7/16”) on this machine.
Using this you can mount additional hardware like a 4th axis or a bench vise.
Overall, the build quality of this machine is quite good.
You also get a lot of upgrade options which makes customization possible.
Harbor freight 44991 can be used on a variety of materials from wood, plastic, and composites to hard metals. However, keep in mind that you have to pair it with the correct tool.
You can do both drilling and milling operations using this machine depending on the tool used.
Workpiece Mounting and Tools
For holding the workpiece on Harbor Freight 44991, you can use a bench vise.
The machine comes with all the mounting mechanisms you will need for this.
Note that the bench vise is not provided with this machine and you have to purchase it seperately.
Harbor Freight 44991 lets you use a drill chuck for drilling and collet for holding milling tools.
Harbor Freight uses a 7/64 inch chuck that can hold bits with a maximum shank of ½ inches and has a drilling capacity of 5 inches.
It comes with the drill chuck and you have to purchase the collets for milling separately based on the endmill you use. An ER collet is a good option for tool holding.
For switching between drill chuck and collet, you only have to open one nut with the provided tool on the top of the machine.
Several videos are available on the internet that you can refer to for a clearer picture of the tool-changing method.
Overall, switching tools on Harbor Freight mini mill is very easy due to the use of an R8 spindle taper which does not require special tools.
The spindle is powered by a 4/5 hp motor and has an R8 taper for holding the cutting tool.
Harbor Freight 44991 can work on two different speed ranges of 0-1100 RPM and 0-2500 RPM. These two modes are labeled on the machine as low and high.
Slower RPM gives more torque with less speed. It is intended for working on high tensile strength materials like steel and strong alloys.
Higher RPM gives less torque with high speed. This high RPM range is intended for soft materials like wood, aluminum, or plastic.
You can switch between these two modes using the lever provided on the machine. There is no need for any tools for switching between the high RPM and low RPM modes.
The mill uses a gear drive system for switching between low and high modes.
The gear used is plastic but that doesn't affect the operation of the machine in any way.
Additionally, third-party metal gears compatible with this mill are available which can replace both the plastic transmission gears with metal ones.
HF 44991 uses a PWM controller for the motor. This lowers the power consumption and increases the life of the motor.
Another advantage of using a PWM system is that the operation of the motor becomes quieter and results in less vibration.
Pairing it with the correct tool and selecting the correct speed will let you work on most of the materials.
Harbor Freight 44991 is a vertical machine and thus the workbed moves on the X and Y axis and the spindle with the cutting tool moves on the Z-axis.
It has an axis travel of 9”, 4”, and 8.5” for X, Y, and Z axes respectively.
Considering that it is a benchtop machine, these values are quite good.
For moving the X and Y axis HF 44991 uses handwheels with 0.0625” (1.59 mm) of linear movement per turn. For the Z-axis this machine uses a knob on the side for large adjustments.
This is the typical resolution in most entry-level hand-operated mills.
For more precise control over the Z-axis Harbor Freight 44991 has a knob on the front which you can engage by pushing the main Z-axis knob until the gear teeth line up.
All three-movement axis have measuring scales with 0.001-inch graduations per scale. The scales are made from metal for higher durability.
Harbor Freight 44991 does not have an unlocking mechanism for the axes. The only way to move the axes is by using handwheels.
It means if you want to move the axis 4 inches at a time, you can only do that by turning the handwheels/knob and moving it gradually with 0.0625" per turn instead of disengaging the mechanism and moving it manually.
There are locks on each of its three-axis to hold it in place while working. An additional hard lock is provided on the Z-axis for safety.
Overall, the axis movement of Harbor Freight 44991 is quite precise, and the handwheel mechanism is also quite responsive.
Dust and Chip Collection
You can easily manage the dust and chips produced by the machine in between operations by using a shop vac.
There is no chip collection tray provided with the machine which means chips will fall on your work table.
However, litllemachineshop has a chip tray in their catalog that you can use with Harbor Freight X2.
A good thing is that all the important parts of the machine like the drive wheel system and spindle are completely covered.
This ensures there is no dust build-up on essential parts.
The spindle used is an air-cooled one and it can run for around 2 to 2.5 hours continuously before you need to stop to let it cool down.
You might need a cooling system for the tool while working with metals.
During long operations on metals, the cutting tool might heat up a lot.
In such a situation you can manually spray a coolant or rig it up with an appropriate cooling system.
Spraying of coolant is recommended during long operation, as this will cool and lubricate the cutting tool as well as the workpiece resulting in a better cut quality.
Overall, you don't need to consider cooling for short runs, but for long runs it's recommended to provide cooling.
For holding the workpiece in place Harbor Freight offers a 4" drill press vise for $23. This vise is made up of cast iron which provides rigidity to it.
The jaws of this vise are replaceable so, you can swap them with any other type if required.
This kit is offered by littlemachineshop for around $198. This replaces the torsion spring system with an air spring one.
Due to the use of belts the machine runs quietly. This also increases the low-speed range to 0-1700 rpm and the high-speed range to 0-4300 rpm.
By installing this you can move your mill head all the way to the top of the machine and down to the lowest point where the hard stop of the z-axis is located.
You can use this rotary table for machining circles. It is even possible to make gears using this (yes!).
You can use the tailstock while using long cylindrical objects. When using long cylindrical objects you need to support the end of the workpiece, a tailstock provides that support.
The rotary table is available on littlemachineshop website for around $534.
The gears for transmission are made of plastic and you can substitute them with metal gears that are compatible with the machine.
The use of metal gears extends the life of the machine. You can get them from littlemachineshop for around $70.
The chip tray is a no-brainer if you want to keep your shop clean.
It is available on littlemachineshop at a cost of around $30.
The HF mini mill comes pre-assembled and is ready to run out of the box.
You also get the tools you need for operating the mill.
Remember to remove the packing grease.
You can apply a rust preventive oil for this. Additionally, the use of oil will also prevent rust build-up on the machine.
A fully printed manual is provided with HF 44991. You can also download a soft copy of the manual from the official website of Harbor Freight.
The manual is well structured with all the safety warnings, precautions, unpacking, installation, operation, and maintenance instructions.
You also get assembly drawings of the X, Y, and Z-axis. This will be helpful while upgrading and repairing the machine.
There's also a parts list of the machine that's useful for beginners.
Additionally, there are a lot of YouTube videos about Harbor Freight 44991. You can refer them if you ever face any issues while using the machine.
HF mini mill is highly popular in the USA, and thus you can find a lot of other users of this mill online.
One such place is the hobby machinist forum.
Harbor Freight 44991 is featured on a lot of YouTube channels of hobbyists and professionals.
From unpacking the machine to all the available upgrades, you can several videos of this mill.
With Harbor Freight 44991, you get a 90 days replacement guarantee from the date of purchase.
You can contact HF through email or phone.
However, for technical support, typically you do not need to contact them as you can get help from online communities and YouTube videos.
Harbor Freight 44991 is an excellent choice for hobbyists and small businesses. You will get a good balance between price and performance.
Harbor Freight 44991 offers a lot of upgrade options that will come in handy when you learn more about machining and want to have more features.
Along with Harbor freight, a lot of third parties also provide spare parts for this machine.
The documentation provided with Harbor Freight 44991 is well written with pictures. You will also get assembly drawings of the X, Y, and Z-axis which will further help in repairs and upgrades.
The community around Harbor Freight 44991 is very strong. You can find a lot of videos around it on YouTube.
Overall, it gives you a bang for your buck and is a good affordable choice for making small parts.
Harbor Freight vs SIEG X2D vs Grizzly G8689
The SIEG X2D and Grizzly G8689 are similar mills and have similar capabilities. However, when it comes to their price HF 44991 beats them hands down.
Although all of them have almost the same features, there are a few minor differences among them.
|Features||HF 44991||SIEG X2D||Grizzly G8689|
|Head tilt||+45°-0°-45°||Solid column||+45°-0°-45°|
|Head support||Torsion spring||Gas strut||Torsion spring|
|Table||3-11/16″ x 15-7/8″||4.7″ x 18.1″||3-5/8″ x 15-3/4″|
|Spindle tapper||R8 tapper||R8 tapper||#3 Morse Taper|
|Spindle speed||0-1100 and 0-2500 RPM||100-1100 and 100-2500 RPM||0-1100 and 0-2500 RPM|
|Face milling capacity||1"||1.2"||1"|
|End milling capacity||1/2"||0.6"||1/2"|
HF 44991 vs SEIG X2D vs Grizzly G8689
The spindle of all these machines has 0.47 hp (350 W) motor and they come with two speed settings high and low.
SIEG X2D uses a solid column and gas strut for its head support which makes this machine the most rigid among the three.
Also, SIEG X2D has a little bit of extra table workbed area compared to the other two mini mills.
The Grizzly G8689 comes with a 1-year manufacturer warranty that covers manufacturing defects, on the Harbor Freight it is only a 90-day replacement guarantee.
But you will need to shell out atleast ~$250 more than Harbor Freight for these added advantages on SIEG and Grizzly.
HF 44991 is a great choice if you are a beginner or a small shop owner who wants to get started with prototyping or light production on a budget.
Frequently Asked Questions (FAQ)
Should I consider buying a used Harbor Freight mini mill?
Yes, you can consider buying a used Harbor Freight mini mill if you are starting with it. However, you should consider buying a new one if you are going to use it as a professional tool in a shop.
Is gear replacement necessary for Harbor Freight Mini Mill?
No, gear replacement is not necessary. The machine will run perfectly fine with those factory-installed gears. However, if you want to operate the machine for a very long time or if your factory-installed gears are broken then you may consider replacing them with metal ones.
Do I need to upgrade to a belt drive system for Harbor Freight Mini Mill?
For hobbyists, this is not something worth spending the extra money on. The machine will run fine with the factory-installed drive system. For professionals, you can consider doing it depending on the type of operations you are performing on it.