This guide reflects how we run industrial moulders daily in a production millwork environment. It is written for operators, supervisors, and production teams, not hobby or light-duty use. The purpose of this page is to create a resource that our employees and others can utilize to learn about operating multi head spindle moulders in a fast paced millwork shop. We believe that if we can provide the resources for our employees to learn, that they will learn faster and become more valuable to the company faster than without those resources.  

Topics overview
1) What is a moulder?
2) How does a moulder work?
3) Determining the amount of the cuts
4) Straightening and flattening blanks
5) Lash
6) Aligning bottom and inside heads
7) Setting the width
8) Setting the thickness
9) Operating overview
10) Double checks
11) Firing up the machine
12) Sending tester sticks
13) Axial versus Radial movements

A moulder is a wood processing machine that utilizes knives mounted in cutterheads installed on spindles to remove material from multiple faces of a board at the same time. The material is fed through the moulder through a series of feed wheels. While there are single head moulders and spindle moulders (also known as shapers), these discussions are based around moulders with 4 or more cutterheads.

The knives in the cutterheads can be straight knives which will produce S4S (surfaced 4 sides) lumber or they may be profiled knives to make tongue and groove boards or crown molding.  Profiled knives are made on a profile grinder.  Some info on profile grinding knives can be found here.

A moulder blank, which is prepared beforehand on other equipment, is fed into the infeed rollers which force it over the bottom cutterhead. This cutterhead removes material from the bottom of the blank and provides a flat reference plane. Additional feed wheels push the piece forward where it receives an inside (right) cut. This cut does two things – provides a 90 degree reference edge to the bottom and also trues up the inside face, meaning it removes some of the wiggle from the board. More feed wheels push the blank to the outside cutterhead. This cutterhead cuts a 90 degree face to the bottom and more importantly, sets the width of the piece. The next cutterhead is the top cutterhead. The top cutterhead sets the thickness of the piece and cuts parallel to the bottom cutterhead. In most 5 head moulders, the final cutterhead is a second bottom head. This head can be used for back reliefs, for back cuts on crown molding, or with a straight cutterhead. We regularly use this cutterhead with straight cutters to take off about .020” from the bottom of the piece so that we remove all traces of the bed lubricant.

For simple profiled cuts, say baseboard or casing, we would keep the first three heads with straight knives. However, the top head would use profiled knives instead of the straight knives. And the 5th bottom head would use a back relief knife versus straight knives. To make tongue and groove paneling, the first bottom, the top, and the last bottom heads would have straight knives, while the side heads would be changed to a tongue profile and a groove profile.

Now that we know that each face of a board will have material removed from it, we have to determine how much material to remove on each cut. To do this, we need to know two things: the thickness and width of the blank, and the thickness and width of the finished product. Let’s say we’re going to cut .75″thick x 3.5″ wide S4S (surfaced 4 sides). We’re going to use rough sawn 4/4 boards that have been ripped to 3.75” wide. What we know is that our blank is 1” thick x 3.75” wide and we also know that our finished product is .75” thick x 3.5” wide. Using quick math, we can subtract the finished product dimensions from the blank dimensions (width: 3.75″ – 3.5″ = 1/4″ removal, thickness 1″ – .75″ = 1/4″ thickness removal) and find that we’ll be removing ¼” of thickness and ¼” of width. For simplicity, we’ll divide those cuts in half between the cutterheads. That means for thickness, we’ll set the first bottom head to remove 1/8” of material which will leave 1/8” of material for the top head to remove. Same thing for the side heads – we’ll set the inside head to remove 1/8” of material and there will be 1/8” of material for the outside head to remove.

In this example, we’ll set the outside head at 3.500” and set the top head at .750”. While the first bottom head and the inside head remove material, they do not set or affect the finished dimensions. This is important to remember. Only the outside head and the top head control the final dimensions.

In this example we did not use the 5th bottom head. As we generally only take a small cut (.020″) with the 5th head, we generally don’t factor it into the calculations for determining how much material to remove with each head.  

For profiled cuts, it is similar. Let’s say we’re going to do crown molding. The top head will have the profiled cutters on them. Let’s say the thickest part of the crown molding is .75″. The formula would be the same – meaning that the bottom cutter would be cutting 1/8″ and the top cutter, at the thickest point in the molding, would be removing 1/8″ also. In the deeper areas of the crown the knives will be removing much more than 1/8″, but we determine our cuts based on the thickest part of the molding. Think of it this way, when you measure a molding for thickness using calipers, where do you measure to? You measure to the thickest part of the molding, right? So when we determine our cuts, we make sure that at the thickest area we’re removing the desired amount of material

When considering how to set up our cuts, one consideration is the minimum amount of removal by the top cutterhead.  This is a consideration because the feed system generally uses steel feed wheels prior to the top head (and then switches to rubber after the top head).  The steel wheels leave marking and/or denting in the top surface of the wood.  If we don’t take a large enough cut to remove these marks, then they will show in the finished face of the product, which would ruin the molding.  For our feed wheels, we find that at the absolute minimum, removing .080″ will clean them up – barely.  .090″ is usually good.  For simplicity sake, we generally figure .100″ as the minimum removal amount for the top head.  

If we have a situation where the blank is thin and we have to remove less than .080″ with the top head, we will swap the infeed wheels to either the knurled metal or rubber.  The knurled metal can be removed with a .060″ cut and the rubber are non-marring, so they don’t mark up the molding at all.  

The bottom and inside heads act just like a jointer would for woodworking. A jointer is used to straighten an edge or a face of a board. The moulder is doing the same thing, except we’re doing it in one pass on the moulder, whereas a board will usually get passed multiple times over a jointer. Just like on jointers, the ability to straighten is directly linked to how long the tables/fences are.

The inside head is a jointing/straightening head – it will straighten out a board up to the thickness of the cut. Meaning, if you’re taking a 1/8” cut, it can straighten up to 1/8” of wiggle. If you push your board up against the infeed fence, you can see usually gaps between the board and the fence. The amount of bite on your cutterhead must be equal or greater to the amount of the largest gap, or the cutterhead won’t make a cut at this area and you’ll be left with rough sawn edges. In our case of the 1×4 S4S above, I’ll generally take a slightly larger cut on the inside head (.150”) and a smaller cut on the outside head (.100”), to give slightly more ability to straighten.

The bottom head is similar – it is a straightening/flattening head for the bottom plane. Set your board on the infeed table and then look for any gaps between the board and the table. Your cut must be greater than the largest gap or the rough sawn edges won’t get cleaned up.

Before we can talk about setting up heads, let’s talk about a dirty little word called lash. Lash, also called backlash, is slop or play between components such as gears and screws. In moulder life, it comes into play when moving heads into position. One of the common mistakes that we see is forgetting to set the heads for lash and then winding up with inconsistent dimensions. 

The heads use a set of machine screws (and/or gears) and nuts to move the cutterheads in/out or up/down. An example of lash is say you’re cranking the outside head in to your final dimension, you accidentally go past it by a hair so you reverse the direction you’re cranking the handle to move the head back towards the outside. However, when you reverse directions with the handle, the head doesn’t immediately move. Maybe you have a ¼ turn, or a ½ turn with no movement. This is the lash. When setting the heads, we must be aware of the lash and account for it otherwise the heads may drift and our tolerances will be off.

To set for lash, we have to understand which direction the head is going to try and move during a cut, and then set or take out the lash to not allow that to happen. Picture this – the knives in the cutterhead are really dull. It’s fighting its way through the wood. In this scenario, there’s a lot of outward force on the cut pushing the head away from the material. Let’s look at the outside head in this scenario. We know if we crank the head in, when we reverse directions, there will be lash. So if we only crank the head in to the final dimension, The lash is still present, meaning the head can move up to the amount of the lash without the handle or gears turning. To remove the lash, we crank past our lash, say we go one full crank past our dimension, then we reverse the direction and come back out to our final dimension. Now the lash is still present, but the only direction it can go is towards the inside, which is not likely to happen since the forces on the cutterhead are pushing it out. This principle applies to all cutterheads.

If you’re familiar with a jointer, you’ve probably done this before. Let’s start with the bottom cutterhead. What we know is that the force of the wood going across the bottom cutterhead is going to try and force it down. So if we raise the head up to alignment, the lash will allow the head to float down a bit. So we must lower the head into final position. For this we will unlock the head and raise it above the outfeed bed (the infeed bed is irrelevant at this point). Use a straight edge laying on the outfeed bed to across the cutterhead. What we’re looking for is to be able to rotate the head with barely any contact on the straight edge. Always rotate away from the direction of the cut to keep from damaging the cutters on the straight edge. I’ll generally set the straight edge in place, hold it with my left hand, and then rotate the cutterhead with my right hand. If it’s still contacting the straight edge, I’ll lower it down a touch and repeat. If your head is way above the surface of the outfeed bed, bring it down to somewhere close before you start rotating and checking. Ultimately, I want to see the straight edge move upwards ever so slightly, and if the cutterhead is rotated in the cutting direction, to move the straight edge forward about 1/8”. You may find that your machine varies slightly from this, but this is a good starting point.

The inside cutterhead is the same. We know that the force of cutting is going to push the head inside (towards the back of the machine), so to properly remove lash, we must finish moving the head in that direction. To do that, we bring the head too far in so that the cutters are way past the outfeed fence, reverse directions, set up our straight edge, and start moving it back to the inside little by little. Just like with the bottom head, we want the knives to just barely contact the straight edge when aligned with the outfeed fence.

We can split this section into 2 groups – machines with counters and machines without counters. Let’s start with machines with counters. The likelihood is that you just ran a profile on this machine and the width was correct. Assuming that’s the case, crank your width out until your desired dimension. With the outside head, to take out lash, you always want to finish while moving towards the outside (making the cut wider). This will generally put you within a few thousands of your dimension, and that can be adjusted after your first test piece.

Moulders without counters. These are trickier to set up, since there’s not a constant reference. Most will have some type of tick marks or measurement on the crank dial, but not an actual counter. The fastest way to set these up is with a set up piece of the dimension you are after. For instance, if you’re setting up to cut 3.5” wide, you would use a scrap piece about a foot long of 3.5” material. Put the material in place against the inside fence and then bring the outside head in against the material. Remove the material, go one more crank in, reverse directions, then go one crank back out. That removed your lash. Put the material back in place, then slowly crank the head out and spin the head backwards until the knives barely contact the board. That will get you within a few thousandths.

You can use the tick marks to dial in the last few thousandths, but you have to know your machine. The tick marks may be metric, which makes translation to thousandths a bit trickier. To get to know your machine, you can set up a dial indicator to determine the distance of each tick mark and/or one full rotation. I will usually write that on the machine nearby with an industrial paint marker so that I have a future reference.

Now your width should be set up.

This can also be broken down into two groups – machines with and without counters. Let’s talk straight knives on machines with counters. This is as easy as it gets. The cutting force will try and push the top head up, so you always want to finish your cut moving the head up. Say you want to go from .750” to .500”. You would crank down past the .500” mark about a turn, crank back up slowly stopping right at .500”. It’s that simple. When changing between profiled and straight cutters, it gets slightly more complicated, but we’ll discuss that in future lessons.

Setting machines without counters is similar to setting the outside head. Use a scrap piece that’s already cut to your desired thickness. As you can imagine, it’s beneficial to have a handful of various thickness pieces available for setup. You would set the piece in place and spin the head until the knives just barely kiss the material.  That should get you within a few thousandths.

There’s a few aspects of operating a moulder in a production environment.  Simplified, the tasks are feeding, catching, and quality control.

Feeding
Feeding the molder is the act of taking the blanks from the stack, putting them on the feed table, and pushing them into the feed wheels of the machine.  Overall a fairly basic task.  When feeding the moulder, I find it critical to review the side grain and align the blank so the prevailing grain creates a downhill cut with the top head.  Basically, we try and reduce the chances of tearing out on the face by orienting the grain properly.  This can get tricky to do at faster feed rates with shorter stock.  The most important part of feeding is keeping the pieces butt to butt – meaning no gap between boards.

Catching
Sometimes you’ll be working in pairs, with one person feeding and one person catching.  This is generally the case with short stock and higher rates of feed, since it’s difficult to run down to the outfeed, stack the moldings on the cart, and get back to the infeed to feed another piece and keep them butt to butt.  However, for any cases where you’re operating the moulder solo, you’ll have to go down to the outfeed, collect, and stack the moldings.  

Quality Control
The operator is fully responsible for the quality control of the finished pieces.  The operator must review the width and thickness, generally with calipers unless the width is greater than 6″, and must review the finish quality of the moldings being produced.  On the finish quality, we’re looking for hard lines from nicked knives, flat spots from the pressure shoe or T, chatter marks, tearout, denting from chips not being extracted, and/or other defects that detract from the overall quality.  In the case of two people on the moulder, the outfeed person (catcher) is in charge of quality control.

Before blindly sending a piece, it’s good to have a checklist to review you’ve adjusted and secured everything before you send a piece through. I find it useful to start at the infeed and work my way toward the back of the machine.

1) Is the infeed fence adjustment correct and locked?
2) Is the infeed bed height set and locked?
3) Is the infeed side pressure element set correctly?
4) Is the bottom head spindle nut tight
5) Is the bottom head properly aligned to the outfeed bed and does it turn freely?
6) Is the inside head nut tight?
7) Is the inside head aligned with the outfeed fence and does it turn freely?
8) Is the side pressure element before the outside head adjusted correctly and tight?
9) Is the outside head spindle nut tight and does the head spin freely?
10) Is the width correct?
11) Is the T adjusted correctly and locked?
12) Is the chipbreaker height and setback correct?
13) Is the top head spindle nut tight?
14) Does the top head spin freely (clearance at bed and chipbreaker)?
15) Is the thickness set correctly?
16) Is the pressure foot adjusted correctly
17) Is the bottom head spindle nut locked?
18) Is the bottom head aligned with the outfeed bed and does it spin freely?
19) Are all of the spindle locks tight including the top head axial (hidden behind top head)
20) Is the feed frame height correct?
21) Are the feed wheels correct for the application and aligned properly?
22) Is the air on?
23) Are the air pressure regulator settings correct?
24) Are the dimensions on the blank correct?
25) Is the feed speed correct? If no, this must be adjusted with the machine running.

After you’ve confirmed your double checks are good, it’s time to fire up the moulder. I generally start with the 1st bottom head and work my way towards the back, finishing with the feed wheels.  Don’t start all of the motors at once.  This creates a massive inrush of electric that can strain the system and starve the motors the power they need to fire up.  Instead, start a motor and listen until it gets up to speed (2 seconds or so).  Once the hum of the head is consistent, fire the next motor.  This staggers the inrush current and allows each motor more power to get up to speed faster.  The longer a motor takes to get up to speed, the more heat it creates, and the faster it dies.

1) Start 1st bottom head
2) Start side heads
3) Start top head
4) Start 5th bottom head (if being used)
5) Start feed motor (adjust feed speed now if necessary)

When firing each head, I like to watch them spool up.  This is a secondary verification (1st is listening to the sound).  If there are clearance issues, the motor may spin but the head will jam creating a belt slippage issue or a motor binding issue.  These are bad situations.  If you fire a motor and the head doesn’t spin, power off immediately.  Let everything stop spinning then review what happened. 

With double checks complete, the moulder heads spinning, and the feed motor on, it’s time to send your first test piece. For testers, we’ll generally use a blank that came off of the gang rip that has defects, say a large knot, that would make it unusable. We’ll generally cut it into 4′ pieces so that we get multiple testers from a single piece. We’ll also cut out the knot so that we don’t risk chipping the knives.  

Slow speed to watch the cuts
For the first piece, I’ll generally have the speed way down, even if I intend to run much faster later. This way I have a little more time to watch the piece pass through each cutterhead. I’ll watch the bottom cut to make sure it’s what I expect and watch how the piece interacts with the feed bed after the bottom head. I’ll watch the inside cut and how the piece interacts with the outfeed fence. You can’t really see the outside head working with the dust hood in place. I may pause the feed as the piece comes under the chipbreaker so that I can snug up the T. I’ll then resume and watch the top head cut. As the piece comes out of the top head, I’ll generally adjust the pressure foot down to minimize chatter. Lastly, I’ll verify the alignment of the final rubber feed wheel(s) to make sure they’re aligned properly and not pushing the piece away from the fence.  

Check your dimensions
As your first piece comes out, you’ll now have exact dimensions. Check your width and thickness with calipers. I don’t like digital calipers. I find them to be less consistent than a true Starrett dial caliper. If your top head has a dial measurement, you can then adjust the dial to the real measurement. Same for your width. Once you’ve adjusted the dial for the real measurement, you can then wind the head in/or or up/down to be the proper measurement.  

Review axial adjustments
Check your profile for axial adjustment. For a basic profile like a casing or baseboard, you’re only looking at top head axial. If you’re doing shiplap or tongue and groove, you’ll be checking your axial with calipers and adjusting both side heads up or down as necessary. Basically you’re checking to make sure the profile is properly aligned to the blank.  

In the previous section, we discussed checking the axial adjustment. What is an axial adjustment? With spindles, we have two types of adjustments that can be made – axial and radial. Axial is a movement parallel to the shaft. Radial is a movement 90 degrees to the shaft. Let’s look at this from the perspective of a top head. Say you’ve got the head set up with a casing profile. When you adjust for thickness, you’re moving the spindle either up or down.  Either direction is 90 degrees from the direction of the spindle, so it classifies as a radial adjustment. When your adjusting the profile in and out to line it up, you’re making axial adjustments.  

For side heads, it’s the same concept – axial is parallel movement and radial is 90 degree movement. Say you’re making tongue and groove paneling, and your groove is being cut by the outside head. You crank the outside head in and out to adjust the width of the piece. This is a radial adjustment. To get the groove centered on the thickness, you’re moving the head up and down. This movement is parallel to the shaft and is an axial movement.  

Axial movements, when you’re aligning a roundover at an edge of a piece, can sometimes be a little bit tricky since there’s no shoulder to measure from to figure out how much to move it. In this case, it’s trial and error with tester pieces.