Kreg Owners' Community


I recently purchased a Kreg Jig. Assorted screws and clamps. In total £150 (approx.$250)

I have read instructions cover to cover and know I am using the correct screws.

These are my problems after drilling a dozen holes in 18mm MDF.

  1. None of the holes are clean with 'fash'  around all the edges.
  2. At least two screws started to bulge the wood and one screw became visible along the edge.
  3. The white plastic plugs do not fit and in my view are too tight. Tried tapping them in but they are clearly too big.

I securely clamped everything. I have made good at the weekend and now at paint stage. Sorry but I didn't think to take photos (too annoyed at the time).

Not a good start. I cannot afford to buy tools that disappoint. However, I am prepared to be educated on the use of the Kreg Jig but I do consider myself to be a competent DIYer!


Andrew Smith

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Hey Andrew, I will take a stab at this.  It is hard since there aren't any photos to go along with.  I have never used the Kreg Jig in MDF and the Kreg screws aren't designed for it.  As far as 18mm, that isn't a true 3/4 inch so you will need to check the depth that you are drilling your pocket holes.  With the plugs, I will be honest, I have never used them and can't comment on that. 

Don't give up on the Kreg just yet!  I have used it on countless projects without fail, I'm sure it's something simple and if you post pics there are plenty of people on this site with more knowledge than myself with the plugs etc.  Also, let us know what you are trying to build and maybe we/I can help.

MDF is not a great material to use with pocket holes. When I used it my holes were fairly clean as I used a high speed corded drill. I did encounter the MDF splitting. So I took the screw out, glued & clamped the split, then carefully put the screw in.

It's not a Kreg jig or Kreg screw issue---

it's the material you selected to use.

I'd suggest using an alternate material.

Use Egyptian Worm Wood from an old Hull

OK. Thank you for your replies.

I get the drift about MDF.

May I respectfully direct you to the many references from KREG and Pocket Holes screws CAN be used with MDF.

Here in the UK we use 'safe' MDF for lots of applications. As with all manufactured wood products the quality can vary though and I am looking at this as being my main problem NOT MDF per se.

I also take the point that 3/4 inch and 18mm are not quite the same (good point).

Finally as no-one seems to have used the white plastic plugs my comments still stands. The design and size needs to be looked at.

Thank you again.



Andrew, speaking from many years of experience using the Kreg Jig and many holes drilled into all types of woods and wood fiber materials I can say that I am pleased with the performance delivered by the Kreg Jig.  I have found that the jig will function well however it takes time to learn the methods of its use.  It differs in different materials.

Providing that you have a quality material in which to work you must also use the proper technique.  In some materials you can bore a pocket hole rapidly and the results will be excellent.  Using the same speeds In other materials, the results will be frustrating and not so good.   You have to alter the speed of the drill and the speed that you feed the drill through the material just like you do when cutting material through a saw.

Of course there are other factors that matter as well such as the sharpness of the tool edge and how brittle is the material you are cutting.

I have bored countless numbers of holes through mdf,  some with great success and others not so good.  The not so good results are often found to be either the quality of the material or my technique was not correct.  To correct the problem I altered my technique to suit the materials.

Although mdf is not my choice of material, in my line of work I do not have the choice as to where I pick one type of material over the other.  I do not like to build cabinets out of melamine, which is a form of Mdf, many customers insist on it use for their own reasons.  The choice I have is to point out to them the differences in mdf and wood but the choice remains in their hands.  The other thing I can do is to be certain that the material I choose is of quanity and that my workmanship is the best I can deliver. 

When I talk of technigue I am refering to the following:

Correct setting ot the jig for the material. This is a topic in its self with many having trouble with the settings.

I have my own method and it does not fail me.  I set the jig up for material thickness and then check it using a nickel on the base and setting the drill bit on top of the nickel and set the debth collar.   It stands to reason if the stop collar stops the bit before it hits the jig base it will not exit the material and will not over bore the pilot hole.  There is one exception to this, It there is chips or dust between the edge of the material and the base of the jig, which will raise the material in the jig the bit will bore too deep and may exit the material edge. 

It is best not to bore through the material and it is best if you do not bore so deep that the bit leaves a dimple on the bottom.This dimple becomes a obstruction between the joining surfaces and will hold your material up off the surface requiring the dimple to have to be crushed in order to get a tight seal. 

Correct clamping of jig to the material.  Flat on the base and 90 degrees to the base. ( no chips between the material and the jig back)  Chips often fall behind the material and get clamped in behind during clamping.

Correct drill RPM speeds for the material.  I use a cord-ed variable speed .  Materials require different RPM speeds to cut the fibers without tearing them out

Correct feed rate (speed in which you push the drill bit through the material)  The bit must have time to cut the material with out tearing through it.

Making sure that chips and dust are not between the jig base and the material which results in a deep pocket hole.

Making sure the jig base is square with the material,  If not you get a crooked pocket hole.

Assembly Time:

When it come time for assembly correct alinement of the screw with the pilot hole is a must to insert a screw accurately.  If not careful the screw will crawl out of the pilot hole and cut its own thread resulting is a screw that has its head not fully seated in the pocket hole.

Speed of the screw insertion. You have to allow the screw to cut its thread with out tearing,  Too fast it will tear out the material and too slow it will also cut out the thread as it goes in.  As a preference I alway use a little glue to act as a lubricant for insertion and as a glue when it dries,  This helps to hold any torn fibers in the screw to material.

Using the correct screw is important.  personally I seldom use a course threaded screw as the thread pitch is just of agressive for some materias.  I have found from experience that the fine thread screw is fine for its purpose.  Look at it this way, would you rather have a thread cut slowly into the fibers or one that is cut so agressive that it tears the fibers reguardless of the screw speed as it is inserted.  If you glue your joints, as is very highly suggested in fiber material, and have a pocket hole with a screw in it, is it not better than the alternative of having a nail driven into the joint. This screw thread topic and insertion speed is of importance as many times the thread pitch and its speed of insertion can actually destroy the ability of the screw to hold the material joint together if it tears out more fibers that it cuts.

Correct tightness of the screw is of importance as well as one that is loose will do little to hold the joint but is still better that one that has bottomed out and either split the material or tore out the material around it threads top a point that it is actually no longer a fasterner but a sore spot on the material and in the mind of the person whom put it there.

To be able to tell you how to put in a screw is something of which only time and experience will teach you.  Learn from your mistakes as they are the best teacher in the first place.  Using the pointers you read and following them will only aid as a guide but it you who feels the screw as it is inserted and sees the results. 

I can only tell you that you have a great tool in your hand and like all things it takes time and use to master its use.  I'm still learning after years of using it.  I will also say I have found no faster method or tool in which to construct a joint between two pieces of material in a simple and speedy method.





If your bulge problem is between the two boards,  you can fix it this way.  After removing the board from the Kreg jig,  drill the screw hole through with a long 1/8" (3mm) drill.  Then countersink where the drill came through.  

The plugs are always too long. They have to be cut flush after they are glued in place. I use a small router with a homemade U shaped base.  The opening in the U is large enough to clear the plug.  Set the router bit just barely short of flush with the bottom of the base. Then run it over the plug.  Or you can cut it flush with a flush cutting saw or sharp chisel. Sand smooth.

Another suggestion for the plug. Set the stop on the drill bit so the drill goes in deeper.   The plug will go in deeper and leave less to remove.  This will leave you with less material under the screw head, so try it in some sample pieces to make sure it will work for you. 

If you set the jig up proerly there will be no bulge or dimple at the point where the screw enters the mating surface. Drilling out the the hole with a drill would not be necessary. The pilot hole will be aproximately 1/8 inch short of exiting the material. With the materials clamped properly together the screw will cut the 1/8 inch out and since it can not get between the mating surfaces it will deposit its self on the screw shank between the threads and the screw head.  the reason for not allowing the bit to cut through and leave a dimple or bulge is to insure that you can mate the two surfaces without any obstruction and thus obtaining a tight joint.

The plugs I agree are too long for the hole and cutting them off is the solution that I, like Michael, use.  I do cut most of the plug off at the bottom end before insertion and finish the cutting on the top using a razor knife if necessary after the glue has dried.  I will not drill the hole deeper as this makes the screw reach longer into the material and sometime is the problem with the screws exiting the material.  If the jig is set correctly the hole should be drilled correctly.  At the very least the drilling of the hole deeper will weaken the upper piece that you are attaching.  In mdf, strength is the important and critical factor.  If you find that the hole is too shallow then the jig is not set properly.  By the same token if the screws are exiting the bottom it is set too deep.

Cutting the plug shorter before inserting it is such an obvious solution that I never thought of it.  Good idea!

Jay Boutwell said:

The plugs I agree are too long for the hole and cutting them off is the solution that I, like Michael, use.  I do cut most of the plug off at the bottom end before insertion and finish the cutting on the top using a razor knife if necessary after the glue has dried.  

Thank you Jay,

I take on board what you have said. I do keep everything clean blowing away any chips and dust.

I am checking the quality of the MDF. I would prefer to use a good quality ply for my sheet material but I am not always able to use this and MDF is what is specified.

I am following all the tutorials and using clamps etc and I am sure I will soon be regarding my Kreg Jig with great affection.

My point about the plugs concerns the plastic type that come with a lip/flange and cannot be cut. Although they are just way too tight and will not seat properly. I chose the plastic plugs because my holes are quite inaccessible and I needed a quick solution. Under normal circumstances I would use timber.

I also feel my Bosch Cordless GSB 18VE-2LI Cordless drill might not be fast enough at 1800rpm. Just bought this also so I cannot afford another drill!

Thanks once again.

Andrew Smith

Mr. Smith,


The major issue that you will be running into is due to the thickness of material you are working with.  Being that it is 18mm is close to 3/4" thick but not quite.  Most people think that this is close enough but when you are working with the severe angles with pocket holes this little amount can make a big difference.  This will be the reason that your screws are bulging and starting to show on the edge.  In order to compensate you will need to adjust your depth collar setting a little bit so that it is not drilling quite as deep.  This will adjust the position of where the screw stops in the pocket hole.  Unfortunately I do not have an exact setting to tell you but some practice with some scrap pieces should allow you to get it close. 


As far as the holes not being clean, this can be cause by one of three things.  First, if you do not have a sharp bit it can cause more tear out to occur since it will be ripping the material out instead of cutting it.  With your kit being new I do not believe this is the case.  Second, it could be due to the grade of material you are working with.  Due to the vast differences in quality of MDF this is quite possible.  The third option could be due to the drill you are using.  We recommend using a drill that has at least 2,000 RPM's.  This allows the bit to cut cleanly and increases the life of your bit.


I was curious if you could supply any pictures of the plugs in the process of being put in.  The plastic caps like you are referring to should slide in without much trouble.  Now they will be snug so they can stay in place without glue but you still should be able to slide them in and out with your hands.  If this is possible please send me a message on here and I will try to see what is going on. 

Thanks KregCS! Another example of the quality customer service provided by Kreg.

I wish more companies paid as much attention to it's customers' concerns as Kreg does.

-- Cheers!

KregCS said:

Mr. Smith,


The major issue that you will be running into is due to the thickness of material you are working with.  Being that it is 18mm is close to 3/4" thick but not quite.  Most people ....

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